Molecular sensor

Last updated
Schematic representation of a chemosensor consisting of a signalling moiety and a recognition moiety that are connected together in some way that facilitates the communication between the two parts. Signalling and recongntion moiety.jpg
Schematic representation of a chemosensor consisting of a signalling moiety and a recognition moiety that are connected together in some way that facilitates the communication between the two parts.

A molecular sensor or chemosensor is a molecular structure (organic or inorganic complexes) that is used for sensing of an analyte to produce a detectable change or a signal. [1] [2] [3] [4] The action of a chemosensor, relies on an interaction occurring at the molecular level, usually involves the continuous monitoring of the activity of a chemical species in a given matrix such as solution, air, blood, tissue, waste effluents, drinking water, etc. The application of chemosensors is referred to as chemosensing, which is a form of molecular recognition. All chemosensors are designed to contain a signalling moiety and a recognition moiety, that is connected either directly to each other or through a some kind of connector or a spacer. [5] [6] [7] The signalling is often optically based electromagnetic radiation, giving rise to changes in either (or both) the ultraviolet and visible absorption or the emission properties of the sensors. Chemosensors may also be electrochemically based. Small molecule sensors are related to chemosensors. These are traditionally, however, considered as being structurally simple molecules and reflect the need to form chelating molecules for complexing ions in analytical chemistry. Chemosensors are synthetic analogues of biosensors, the difference being that biosensors incorporate biological receptors such as antibodies, aptamers or large biopolymers.

Contents

Illustration of the common models used in sensor construction. F-S-R models.jpg
Illustration of the common models used in sensor construction.

Chemosensors describes molecule of synthetic origin that signal the presence of matter or energy. A chemosensor can be considered as type of an analytical device. Chemosensors are used in everyday life and have been applied to various areas such as in chemistry, biochemistry, immunology, physiology, etc. and within medicine in general, such as in critical care analysis of blood samples. Chemosensors can be designed to detect/signal a single analyte or a mixture of such species in solution. [4] [8] [9] [10] [11] This can be achieved through either a single measurement or through the use of continuous monitoring. The signalling moiety acts as a signal transducer, converting the information (recognition event between the chemosensor and the analyte) into an optical response in a clear and reproducible manner.

Most commonly, the change (the signal) is observed by measuring the various physical properties of the chemosensor, such as the photo-physical properties seen in the absorption or emission, where different wavelengths of the electromagnetic spectrum are used. [12] [13] Consequently, most chemosensors are described as being either colorimetric (ground state) or luminescent (excited state, fluorescent or phosphorescent). Colorimetric chemosensors give rise to changes in their absorption properties (recorded using ultraviolet–visible spectroscopy), such as in absorption intensity and wavelength or in chirality (using circularly polarized light, and CD spectroscopy). [14]

SelectiveHeparinBinding.png SelectiveTannineBinding.png

SaxitoxinSensor.png

Heparin binding Tannic acid binding Saxitoxin binding

In contrast, then in the case of luminescent chemosensors, the detection of an analyte, using fluorescence spectroscopy, gives rise to spectral changes in the fluorescence excitation or in the emission spectra, which are recorded using a fluorimeter. [15] Such changes can also occur in other excited state properties such as in the excited state life-time(s), quantum yield of fluorescence, and polarisation, etc. of the chemosensor. Fluorescence detection can be achieved at a low concentration (below ~ 10-6 M) with most fluorescence spectrometers. This offers the advantage of using the sensors directly within fibre optic systems. Examples of the use of chemosensors are to monitor blood content, drug concentrations, etc., as well as in environmental samples. Ions and molecules occur in abundance in biological and environmental systems where they are involved/effete biological and chemical processes. [16] The development of molecular chemosensors as probes for such analytes is an annual multibillion-dollar business involving both small SMEs as well as large pharmaceutical and chemical companies.

Left: Example of the change observed in the colorimetric azobenzene based chemosensor 1 in pH 7.4 solution upon recognition of copper ion. The recognition/sensing event being communicated as a clear change in colour that is visible to the naked eye. Right: The corresponding changes in the UV-visible absorption spectrum of the chemosensor upon recognition/binding to Cu(II) (shown in blue) and from the free sensor (shown in green). The changes after adding EDTA reverse the changes result in the formation of original spectra (shown in red). Colorimetic sensor for Cu(II).jpg
Left: Example of the change observed in the colorimetric azobenzene based chemosensor 1 in pH 7.4 solution upon recognition of copper ion. The recognition/sensing event being communicated as a clear change in colour that is visible to the naked eye. Right: The corresponding changes in the UV-visible absorption spectrum of the chemosensor upon recognition/binding to Cu(II) (shown in blue) and from the free sensor (shown in green). The changes after adding EDTA reverse the changes result in the formation of original spectra (shown in red).

Chemosensors were first used to describe the combination of a molecular recognition with some form of reporter so the presence of a guest can be observed (also referred to as the analyte, c.f. above). [17] Chemosensors are designed to contain a signalling moiety and a molecular recognition moiety (also called the binding site or a receptor). Combining both of these components can be achieved in a number of ways, such as integrated, twisted or spaced. Chemosensors are consider as major component of the area of molecular diagnostics, within the discipline of supramolecular chemistry, which relies on molecular recognition. In terms of supramolecular chemistry, chemosensing is an example of host–guest chemistry, where the presence of a guest (the analyte) at the host site (the sensor) gives rise to recognition event (e.g. sensing) that can be monitored in real time. This requires the binding of the analyte to the receptor, using all kinds of binding interactions such as hydrogen bonding, dipole- and electrostatic interactions, solvophobic effect, metal chelation, etc. The recognition/binding moiety is responsible for selectivity and efficient binding of the guest/analyte, which depend on ligand topology, characteristics of the target (ionic radius, size of molecule, chirality, charge, coordination number and hardness, etc.) and the nature of the solvent (pH, ionic strength, polarity). Chemosensors are normally developed to be able to interact with the target species in reversible manner, which is a prerequisite for continuous monitoring.

One of the first examples of a fluorescent chemosensor developed for anion monitoring (phosphate) in competitive aqueous media. The chemosensors is not emissive in its 'free' form A, but upon recognition of the phosphate by the polyamine receptor moiety (through mixture of electrostatic and hydrogen bonding interactions) B, the fluorescence emission is gradually enhanced, resulting eventually in the formation of a highly fluorescent (host:guest) structure C. Phosphate sensing.jpg
One of the first examples of a fluorescent chemosensor developed for anion monitoring (phosphate) in competitive aqueous media. The chemosensors is not emissive in its 'free' form A, but upon recognition of the phosphate by the polyamine receptor moiety (through mixture of electrostatic and hydrogen bonding interactions) B, the fluorescence emission is gradually enhanced, resulting eventually in the formation of a highly fluorescent (host:guest) structure C.

Optical signalling methods (such as fluorescence) are sensitive and selective, and provide a platform for real-time response, and local observation. As chemosensors are designed to be both targeting (i.e. can recognize and bind a specific species) and sensitive to various concentration ranges, they can be used to observed real-live events on the cellular level. As each molecule can give rise to a signal/readout, that can be selectively measured, chemosensors are often said to be non-invasive and consequently have attracted significant attentions for their applications within biological matter, such as within living cells. Many examples of chemosensors have been developed for observing cellular function and properties, including monitoring ion flux concentrations and transports within cells such as Ca(II), Zn(II), Cu(II) and other physiologically important cations [18] and anions, [19] as well as biomolecules. [20] [21]

The design of ligands for the selective recognition of suitable guests such as metal cations [22] and anions [23] [24] has been an important goal of supramolecular chemistry. The term supramolecular analytical chemistry has recently been coined to describe the application of molecular sensors to analytical chemistry. [25] Small molecule sensors are related to chemosensors. However, these are traditionally considered as being structurally simple molecules and reflect the need to form chelating molecules for complexing ions in analytical chemistry.

History

While chemosensors were first defined in the 1980s, the first example of such a fluorescent chemosensor can be documented to be that of Friedrich Goppelsroder, who in 1867, developed a method for the determination/sensing of aluminium ion, using fluorescent ligand/chelate. This and subsequent work by others, gave birth to what is considered as modern analytical chemistry.

In the 1980s the development of chemosensing was achieved by Anthony W. Czarnik, [26] [27] [28] A. Prasanna de Silva [29] [30] [31] and Roger Tsien, [32] [33] [34] who developed various types of luminescent probes for ions and molecules in solutions and within biological cells, for real-time applications. Tsien went on to study and developing this area of research further by developing and studding fluorescent proteins for applications in biology, such as green fluorescent proteins (GFP) for which he was awarded the Nobel Prize in Chemistry in 2008. The work of Lynn Sousa in the late 1970s, on the detection of alkali metal ions, possibly resulting in one of the first examples of the use of supramolecular chemistry in fluorescent sensing design, [35] as well as that of J.-M. Lehn, H. Bouas-Laurent and co-workers at Université Bordeaux I, France. [36] The development of PET sensing of transition metal ions was developed by L. Fabbrizzi, among others. [37]

In chemosensing, the use of fluorophore connected to the receptor via a covalent spacer is now commonly referred to as fluorophores-spacer-receptor principle. In such systems, the sensing event is normally described as being due to changes in the photophysical properties of the chemosensor systems due to chelation induced enhanced fluorescence (CHEF), [26] [27] [28] and photoinduced electron transfer (PET), [29] [30] [31] mechanisms. In principle the two mechanisms are based on the same idea; the communication pathway is in the form of a through-space electron transfer from the electron rich receptors to the electron deficient fluorophores (through space). This results in fluorescence quenching (active electron transfer), and the emission from the chemosensor is 'switched off,' for both mechanisms in the absence of the analytes. However, upon forming a host–guest complex between the analyte and receptor, the communication pathway is broken and the fluorescence emission from the fluorophores is enhanced, or 'switched on'. In other words, the fluorescence intensity and quantum yield are enhanced upon analyte recognition.

Left: Example of the changes in the fluorescence emission spectra of a chemosensor for zinc, where the emission is enhanced or 'switched on' upon recognition of the zinc ion in buffered solution. Right: the changes under a UV lamp demonstrating the striking difference in the luminescence emission upon addition of Zn(II): left valve in the absence (free chemosensor) right in the presence of Zn(II). Flurescent Zn sensor 5.jpg
Left: Example of the changes in the fluorescence emission spectra of a chemosensor for zinc, where the emission is enhanced or 'switched on' upon recognition of the zinc ion in buffered solution. Right: the changes under a UV lamp demonstrating the striking difference in the luminescence emission upon addition of Zn(II): left valve in the absence (free chemosensor) right in the presence of Zn(II).

The fluorophores-receptor can also be integrated within the chemosensor. This leads to changes in the emission wavelength, which often results in change in colour. When the sensing event results in the formation of a signal that is visible to the naked eye, such sensors are normally referred to as colorimetric. Many examples of colorimetric chemosensors for ions such as fluoride have been developed. [38] A pH indicator can be consider as a colorimetric chemosensors for protons. Such sensors have been developed for other cations, as well as anions and larger organic and biological molecules, such as proteins and carbohydrates. [39]

Design principles

Chemosensors are nano-sized molecules and for application in vivo need to be non-toxic. A chemosensor must be able to give a measurable signal in direct response to the analyte recognition. Hence, the signal response is directly related to the magnitude of the sensing event (and, in turn concentration of the analyte). While the signalling moiety acts as a signal transducer, converting the recognition event into an optical response. The recognition moiety is responsible for binding to the analyte in a selective and reversible manner. If the binding sites are 'irreversible chemical reactions,' the indicators are described as fluorescent chemodosimeters, or fluorescent probes.

An active communication pathway has to be open between the two moieties for the sensor to operate. In colorimetric chemosensors, this usually relies on the receptor and transducer to be structurally integrated. In luminescent/fluorescent chemosensing these two parts can be 'spaced' out or connected with a covalent spacer. The communication pathway is through electron transfer or energy transfer for such fluorescent chemosensors. The effectiveness of the host–guest recognition between the receptor and the analyte depends on several factors, including the design of the receptor moiety, which is objective is to match as much the nature of the structural nature of the target analyte, as well as the nature of the environment that the sensing event occurs within (e.g. the type of media, i.e. blood, saliva, urine, etc. in biological samples). An extension to this approach is the development of molecular beacons, which are oligonucleotide hybridization probes based on fluorescence signalling where the recognition or the sensing event is communicated through enhancement or reduction in luminescence through the use of Förster resonance energy transfer (FRET) mechanism.

Fluorescent chemosensing

All chemosensors are designed to contain a signalling moiety and a recognition moiety. These are integrated directly or connected with a short covalent spacer depending on the mechanism involved in the signalling event. The chemosensor can be based on self-assembly of the sensor and the analyte. An example of such a design are the (indicator) displacement assays IDA. [40] IDA sensor for anions such as citrate or phosphate ions have been developed whereby these ions can displace a fluorescent indicator in an indicator-host complex. [5] The so-called UT taste chip (University of Texas) is a prototype electronic tongue and combines supramolecular chemistry with charge-coupled devices based on silicon wafers and immobilized receptor molecules.

Most examples of chemosensors for ions, such as those of alkali metal ions (Li+, Na+, K+, etc.) and alkali earth metal ions (Mg2+, Ca2+, etc.) are designed so that the excited state of the fluorophore component of the chemosensor is quenched by an electron transfer when the sensor is not complexed to these ions. No emission is thus observed, and the sensor is sometimes referred to as being 'switched off'. By complexing the sensor with a cation, the conditions for electron transfer are altered so that the quenching process is blocked, and fluorescence emission is 'switched on'. The probability of PET is governed by the overall free energy of the system (the Gibbs free energy ΔG). The driving force for PET is represented by ΔGET, the overall changes in the free energy for the electron transfer can be estimated using the Rehm-Weller equation. [41] Electron transfer is distance dependent and decreases with increasing spacer length. Quenching by electron transfer between uncharged species leads to the formation of a radical ion pair. This is sometimes referred to as being the primary electron transfer. The possible electron transfer, which takes place after the PET, is referred to as the 'secondary electron transfer'. Chelation Enhancement Quenching (CHEQ) is the opposite effect seen for CHEF. [42] In CHEQ, a reduction is observed in fluorescent emission of the chemosensor in comparison to that seen the originally for the 'free' sensor upon host–guest formation. As electron transfer is directional, such systems have also been described by the PET principle, being described as an enhancement in PET from the receptor to the fluorophore with enhanced degree of quenching. Such an effect has been demonstrated for the sensing of anions such as carboxylates and fluorides. [43]

A large number of examples of chemosensors have been developed by scientists in physical, life and environmental sciences. The advantages of fluorescence emission being 'switched on' from 'off' upon the recognition event enabling the chemosensors to be compared to 'beacons in the night'. As the process is reversible, the emission enhancement is concentration dependent, only becoming 'saturated' at high concentrations (fully bound receptor). Hence, a correlation can be made between luminescence (intensity, quantum yield and in some cases lifetime) and the analyte concentration. Through careful design, and evaluation of the nature of the communication pathway, similar sensors based on the use of 'on-off' switching, or 'on-off-on,' or 'off-on-off' switching have been designed. The incorporation of chemosensors onto surfaces, such as quantum dots, nanoparticles, or into polymers is also a fast-growing area of research. [44] [45] [46] Fluorescence sensing has also been combined with electrochemical techniques, conferring the advantages of both methods. [47] Other examples of chemosensors that work on the principle of switching fluorescent emission either on or off include, Förster resonance energy transfer (FRET), internal charge transfer (ICT), twisted internal charge transfer (TICT), metal-based emission (such as in lanthanide luminescence), [48] [49] and excimer and exciplex emission and aggregation-induced emission (AIE). [50] [51] Chemosensors were one of the first examples of molecules that could result in switching between 'on' or 'off' states through the use of external stimuli and as such can be classed as synthetic molecular machine, to which the Nobel Prize in Chemistry was awarded to in 2016 to Jean-Pierre Sauvage, Fraser Stoddart and Bernard L. Feringa.

The application of these same design principles used in chemosensing also paved the way for the development of molecular logic gates mimics (MLGMs), [52] [53] being first proposed using PET based fluorescent chemosensors by de Silva and co-workers in 1993. [54] Molecules have been made to operate in accordance with Boolean algebra that performs a logical operation based on one or more physical or chemical inputs. The field has advanced from the development of simple logic systems based on a single chemical input to molecules capable of carrying out complex and sequential operations.

Applications of Chemosensors

POTI Critical Care Analyser developed for the sensing of various ions and molecules that are important for critical care analysis of blood samples. This kind of analyser is used in ambulances and hospitals around the world. This system is based on monitoring the changes in various chemosensors through modulation in their fluorescence properties. OPTI Medical Systems.jpg
POTI Critical Care Analyser developed for the sensing of various ions and molecules that are important for critical care analysis of blood samples. This kind of analyser is used in ambulances and hospitals around the world. This system is based on monitoring the changes in various chemosensors through modulation in their fluorescence properties.

Chemosensors have been incorporated through surface functionalization onto particles and beads such as metal based nanoparticles, quantum dots, carbon-based particles and into soft materials such as polymers to facilitate their various applications.

Other receptors are sensitive not to a specific molecule but to a molecular compound class, these chemosensors are used in array- (or microarray) based sensors. Array-based sensors utilise analyte binding by the differential receptors. One example is the grouped analysis of several tannic acids that accumulate in ageing Scotch whisky in oak barrels. The grouped results demonstrated a correlation with the age but the individual components did not. A similar receptor can be used to analyze tartrates in wine.

The application of chemosensors in cellular imaging is particularly promising as most biological process are now monitored by using imaging technologies such as confocal fluorescence and superresolution microscopy, among others.

Fluorescence chemosensor/probe for monitoring enzymatic activity using confocal fluorescence microscopy. a) The probe is not luminescent and not delivered into cells. b)The sugar unit is recognised by a glycosidase which cleaves it off and releases the chemosensor into cells. Enzyme realsse of preprobe.jpg
Fluorescence chemosensor/probe for monitoring enzymatic activity using confocal fluorescence microscopy. a) The probe is not luminescent and not delivered into cells. b)The sugar unit is recognised by a glycosidase which cleaves it off and releases the chemosensor into cells.

The compound saxitoxin is a neurotoxin found in shellfish and a chemical weapon. An experimental sensor for this compound is again based on PET. Interaction of saxitoxin with the sensor's crown ether moiety kills its PET process towards the fluorophore and fluorescence is switched from off to on. [4] The unusual boron moiety makes sure the fluorescence takes place in the visible light part of the electromagnetic spectrum.

See also

Related Research Articles

<span class="mw-page-title-main">Fluorescence</span> Emission of light by a substance that has absorbed light

Fluorescence is the emission of light by a substance that has absorbed light or other electromagnetic radiation. It is a form of luminescence. In most cases, the emitted light has a longer wavelength, and therefore a lower photon energy, than the absorbed radiation. A perceptible example of fluorescence occurs when the absorbed radiation is in the ultraviolet region of the electromagnetic spectrum, while the emitted light is in the visible region; this gives the fluorescent substance a distinct color that can only be seen when the substance has been exposed to UV light. Fluorescent materials cease to glow nearly immediately when the radiation source stops, unlike phosphorescent materials, which continue to emit light for some time after.

<span class="mw-page-title-main">Fluorescent tag</span>

In molecular biology and biotechnology, a fluorescent tag, also known as a fluorescent label or fluorescent probe, is a molecule that is attached chemically to aid in the detection of a biomolecule such as a protein, antibody, or amino acid. Generally, fluorescent tagging, or labeling, uses a reactive derivative of a fluorescent molecule known as a fluorophore. The fluorophore selectively binds to a specific region or functional group on the target molecule and can be attached chemically or biologically. Various labeling techniques such as enzymatic labeling, protein labeling, and genetic labeling are widely utilized. Ethidium bromide, fluorescein and green fluorescent protein are common tags. The most commonly labelled molecules are antibodies, proteins, amino acids and peptides which are then used as specific probes for detection of a particular target.

A biosensor is an analytical device, used for the detection of a chemical substance, that combines a biological component with a physicochemical detector. The sensitive biological element, e.g. tissue, microorganisms, organelles, cell receptors, enzymes, antibodies, nucleic acids, etc., is a biologically derived material or biomimetic component that interacts with, binds with, or recognizes the analyte under study. The biologically sensitive elements can also be created by biological engineering. The transducer or the detector element, which transforms one signal into another one, works in a physicochemical way: optical, piezoelectric, electrochemical, electrochemiluminescence etc., resulting from the interaction of the analyte with the biological element, to easily measure and quantify. The biosensor reader device connects with the associated electronics or signal processors that are primarily responsible for the display of the results in a user-friendly way. This sometimes accounts for the most expensive part of the sensor device, however it is possible to generate a user friendly display that includes transducer and sensitive element. The readers are usually custom-designed and manufactured to suit the different working principles of biosensors.

<span class="mw-page-title-main">Fluorophore</span> Agents that emit light after excitation by light

A fluorophore is a fluorescent chemical compound that can re-emit light upon light excitation. Fluorophores typically contain several combined aromatic groups, or planar or cyclic molecules with several π bonds.

Nanosensors are nanoscale devices that measure physical quantities and convert these to signals that can be detected and analyzed. There are several ways proposed today to make nanosensors; these include top-down lithography, bottom-up assembly, and molecular self-assembly. There are different types of nanosensors in the market and in development for various applications, most notably in defense, environmental, and healthcare industries. These sensors share the same basic workflow: a selective binding of an analyte, signal generation from the interaction of the nanosensor with the bio-element, and processing of the signal into useful metrics.

Supramolecular chemistry refers to the branch of chemistry concerning chemical systems composed of a discrete number of molecules. The strength of the forces responsible for spatial organization of the system range from weak intermolecular forces, electrostatic charge, or hydrogen bonding to strong covalent bonding, provided that the electronic coupling strength remains small relative to the energy parameters of the component. While traditional chemistry concentrates on the covalent bond, supramolecular chemistry examines the weaker and reversible non-covalent interactions between molecules. These forces include hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, pi–pi interactions and electrostatic effects.

<span class="mw-page-title-main">Molecular recognition</span> Type of non-covalent bonding

The term molecular recognition refers to the specific interaction between two or more molecules through noncovalent bonding such as hydrogen bonding, metal coordination, hydrophobic forces, van der Waals forces, π-π interactions, halogen bonding, or resonant interaction effects. In addition to these direct interactions, solvents can play a dominant indirect role in driving molecular recognition in solution. The host and guest involved in molecular recognition exhibit molecular complementarity. Exceptions are molecular containers, including, e.g., nanotubes, in which portals essentially control selectivity.

<span class="mw-page-title-main">Host–guest chemistry</span> Supramolecular structures held together other than by covalent bonds

In supramolecular chemistry, host–guest chemistry describes complexes that are composed of two or more molecules or ions that are held together in unique structural relationships by forces other than those of full covalent bonds. Host–guest chemistry encompasses the idea of molecular recognition and interactions through non-covalent bonding. Non-covalent bonding is critical in maintaining the 3D structure of large molecules, such as proteins and is involved in many biological processes in which large molecules bind specifically but transiently to one another.

<span class="mw-page-title-main">Quenching (fluorescence)</span> Reduction of light emitted from fluorescent substances

In chemistry, quenching refers to any process which decreases the fluorescent intensity of a given substance. A variety of processes can result in quenching, such as excited state reactions, energy transfer, complex-formation and collisions. As a consequence, quenching is often heavily dependent on pressure and temperature. Molecular oxygen, iodine ions and acrylamide are common chemical quenchers. The chloride ion is a well known quencher for quinine fluorescence. Quenching poses a problem for non-instant spectroscopic methods, such as laser-induced fluorescence.

A ChemFET is a chemically-sensitive field-effect transistor, that is a field-effect transistor used as a sensor for measuring chemical concentrations in solution. When the target analyte concentration changes, the current through the transistor will change accordingly. Here, the analyte solution separates the source and gate electrodes. A concentration gradient between the solution and the gate electrode arises due to a semi-permeable membrane on the FET surface containing receptor moieties that preferentially bind the target analyte. This concentration gradient of charged analyte ions creates a chemical potential between the source and gate, which is in turn measured by the FET.

In chemistry, mechanically interlocked molecular architectures (MIMAs) are molecules that are connected as a consequence of their topology. This connection of molecules is analogous to keys on a keychain loop. The keys are not directly connected to the keychain loop but they cannot be separated without breaking the loop. On the molecular level, the interlocked molecules cannot be separated without the breaking of the covalent bonds that comprise the conjoined molecules; this is referred to as a mechanical bond. Examples of mechanically interlocked molecular architectures include catenanes, rotaxanes, molecular knots, and molecular Borromean rings. Work in this area was recognized with the 2016 Nobel Prize in Chemistry to Bernard L. Feringa, Jean-Pierre Sauvage, and J. Fraser Stoddart.

A molecular logic gate is a molecule that performs a logical operation based on one or more physical or chemical inputs and a single output. The field has advanced from simple logic systems based on a single chemical or physical input to molecules capable of combinatorial and sequential operations such as arithmetic operations. Molecular logic gates work with input signals based on chemical processes and with output signals based on spectroscopic phenomena.

<span class="mw-page-title-main">BODIPY</span> Parent chemical compound of the BODYPY fluorescent dyes

BODIPY is the technical common name of a chemical compound with formula C
9H
7BN
2F
2, whose molecule consists of a boron difluoride group BF
2 joined to a dipyrromethene group C
9H
7N
2; specifically, the compound 4,4-difluoro-4-bora-3a,4a-diaza-s-indacene in the IUPAC nomenclature. The common name is an abbreviation for "boron-dipyrromethene". It is a red crystalline solid, stable at ambient temperature, soluble in methanol.

<span class="mw-page-title-main">Fluorescence in the life sciences</span> Scientific investigative technique

Fluorescence is used in the life sciences generally as a non-destructive way of tracking or analysing biological molecules. Some proteins or small molecules in cells are naturally fluorescent, which is called intrinsic fluorescence or autofluorescence. Alternatively, specific or general proteins, nucleic acids, lipids or small molecules can be "labelled" with an extrinsic fluorophore, a fluorescent dye which can be a small molecule, protein or quantum dot. Several techniques exist to exploit additional properties of fluorophores, such as fluorescence resonance energy transfer, where the energy is passed non-radiatively to a particular neighbouring dye, allowing proximity or protein activation to be detected; another is the change in properties, such as intensity, of certain dyes depending on their environment allowing their use in structural studies.

Lanthanide probes are a non-invasive analytical tool commonly used for biological and chemical applications. Lanthanides are metal ions which have their 4f energy level filled and generally refer to elements cerium to lutetium in the periodic table. The fluorescence of lanthanide salts is weak because the energy absorption of the metallic ion is low; hence chelated complexes of lanthanides are most commonly used. The term chelate derives from the Greek word for “claw,” and is applied to name ligands, which attach to a metal ion with two or more donor atoms through dative bonds. The fluorescence is most intense when the metal ion has the oxidation state of 3+. Not all lanthanide metals can be used and the most common are: Sm(III), Eu(III), Tb(III), and Dy(III).

<span class="mw-page-title-main">Small molecule sensors</span>

Small molecule sensors are an effective way to detect the presence of metal ions in solution. Although many types exist, most small molecule sensors comprise a subunit that selectively binds to a metal that in turn induces a change in a fluorescent subunit. This change can be observed in the small molecule sensor's spectrum, which can be monitored using a detection system such as a microscope or a photodiode. Different probes exist for a variety of applications, each with different dissociation constants with respect to a particular metal, different fluorescent properties, and sensitivities. They show great promise as a way to probe biological processes by monitoring metal ions at low concentrations in biological systems. Since they are by definition small and often capable of entering biological systems, they are conducive to many applications for which other more traditional bio-sensing are less effective or not suitable.

Diketopyrrolopyrroles (DPPs) are organic dyes and pigments based on the heterocyclic dilactam 2,5-dihydropyrrolo[3,4-c]pyrrole-1,4-dione, widely used in optoelectronics. DPPs were initially used as pigments in the painting industry due to their high resistance to photodegradation. More recently, DPP derivatives have been also investigated as promising fluorescent dyes for bioimaging applications, as well as components of materials for use in organic electronics.

Thermally activated delayed fluorescence (TADF) is a process through which a molecular species in a non-emitting excited state can incorporate surrounding thermal energy to change states and only then undergo light emission. The TADF process usually involves an excited molecular species in a triplet state, which commonly has a forbidden transition to the ground state termed phosphorescence. By absorbing nearby thermal energy the triplet state can undergo reverse intersystem crossing (RISC) converting it to a singlet state, which can then de-excite to the ground state and emit light in a process termed fluorescence. Along with fluorescent and phosphorescent compounds, TADF compounds are one of the three main light-emitting materials used in organic light-emitting diodes (OLEDs). Although most TADF molecules rely on the RISC from a triplet state to a singlet state, some of them take advantage of RISC processes between states with other spin multiplicities instead, for example from a quartet state to a doublet state.

<span class="mw-page-title-main">Anthony Czarnik</span> American biochemist and inventor

Anthony W. Czarnik is an American chemist and inventor. He is best known for pioneering studies in the field of fluorescent chemosensors and co-founding Illumina, Inc., a biotechnology company in San Diego. Czarnik was also the founding editor of ACS Combinatorial Science. He currently serves as an adjunct visiting professor at the University of Nevada, Reno.

A chemical sensor array is a sensor architecture with multiple sensor components that create a pattern for analyte detection from the additive responses of individual sensor components. There exist several types of chemical sensor arrays including electronic, optical, acoustic wave, and potentiometric devices. These chemical sensor arrays can employ multiple sensor types that are cross-reactive or tuned to sense specific analytes.

References

  1. ↑ Wu, Di; Sedgwick, Adam C.; Gunnlaugsson, Thorfinnur; Akkaya, Engin U.; Yoon, Juyoung; James, Tony D. (2017-12-07). "Fluorescent chemosensors: the past, present and future". Chemical Society Reviews. 46 (23): 7105–7123. doi: 10.1039/c7cs00240h . hdl: 2262/91692 . ISSN   1460-4744. PMID   29019488.
  2. ↑ Wang, Binghe; Anslyn, Eric V. (2011-08-24). Chemosensors: Principles, Strategies, and Applications. John Wiley & Sons. doi:10.1002/9781118019580. ISBN   9781118019573.
  3. ↑ Czarnik, Anthony W. (1994-10-01). "Chemical Communication in Water Using Fluorescent Chemosensors". Accounts of Chemical Research. 27 (10): 302–308. doi:10.1021/ar00046a003. ISSN   0001-4842.
  4. 1 2 3 de Silva, A. Prasanna; Gunaratne, H. Q. Nimal; Gunnlaugsson, Thorfinnur; Huxley, Allen J. M.; McCoy, Colin P.; Rademacher, Jude T.; Rice, Terence E. (1997-08-05). "Signaling Recognition Events with Fluorescent Sensors and Switches". Chemical Reviews. 97 (5): 1515–1566. doi:10.1021/cr960386p. PMID   11851458.
  5. 1 2 Czarnik, Anthony W. (1993). Fluorescent Chemosensors for Ion and Molecule Recognition – ACS Symposium Series (ACS Publications). Vol. 538. doi:10.1021/bk-1993-0538. ISBN   0-8412-2728-4.
  6. ↑ Bissell, Richard A.; Silva, A. Prasanna de; Gunaratne, H. Q. Nimal; Lynch, P. L. Mark; Maguire, Glenn E. M.; Sandanayake, K. R. A. Samankumara (1992-01-01). "Molecular fluorescent signalling with 'fluor–spacer–receptor' systems: approaches to sensing and switching devices via supramolecular photophysics". Chem. Soc. Rev. 21 (3): 187–195. doi:10.1039/cs9922100187. ISSN   1460-4744.
  7. ↑ Desvergne, J. P.; Czarnik, A. W. (1997-04-30). Chemosensors of Ion and Molecule Recognition. Springer Science & Business Media. ISBN   9780792345558.
  8. ↑ F., Callan, J.; P., de Silva, A.; C., Magri, D. (2005). "Luminescent sensors and switches in the early 21st century" . Tetrahedron. 61 (36): 8551–8588. doi:10.1016/j.tet.2005.05.043. ISSN   0040-4020.{{cite journal}}: CS1 maint: multiple names: authors list (link)
  9. ↑ de Silva, A. P.; Fox, D. B.; Moody, T. S.; Weir, S. M. (January 2001). "The development of molecular fluorescent switches". Trends in Biotechnology. 19 (1): 29–34. doi:10.1016/S0167-7799(00)01513-4. ISSN   0167-7799. PMID   11146100.
  10. ↑ Supramolecular chemistry : from molecules to nanomaterials. Chichester, West Sussex: Wiley. 2012. ISBN   9780470746400. OCLC   753634033.
  11. ↑ Fabbrizzi, Luigi; Licchelli, Maurizio; Pallavicini, Piersandro (1999-10-01). "Transition Metals as Switches". Accounts of Chemical Research. 32 (10): 846–853. doi:10.1021/ar990013l. ISSN   0001-4842.
  12. ↑ Turro, Nicholas J. (1991). Modern Molecular Photochemistry. University Science Books. ISBN   9780935702712.
  13. ↑ Balzani, Vincenzo (1990). Supramolecular photochemistry. New York: Ellis Horwood. ISBN   978-0138775315. OCLC   22183798.
  14. ↑ Daly, Brian; Ling, Jue; Silva, A. Prasanna de (2015-06-22). "Current developments in fluorescent PET (photoinduced electron transfer) sensors and switches". Chemical Society Reviews. 44 (13): 4203–4211. doi:10.1039/C4CS00334A. ISSN   1460-4744. PMID   25695939. S2CID   197269304.
  15. ↑ Duke, Rebecca M.; Veale, Emma B.; Pfeffer, Frederick M.; Kruger, Paul E.; Gunnlaugsson, Thorfinnur (2010-09-17). "Colorimetric and fluorescent anion sensors: an overview of recent developments in the use of 1,8-naphthalimide-based chemosensors". Chemical Society Reviews. 39 (10): 3936–53. doi:10.1039/B910560N. hdl: 2262/67324 . ISSN   1460-4744. PMID   20818454.
  16. ↑ Que, Emily L.; Domaille, Dylan W.; Chang, Christopher J. (2008-05-01). "Metals in Neurobiology: Probing Their Chemistry and Biology with Molecular Imaging". Chemical Reviews. 108 (5): 1517–1549. doi:10.1021/cr078203u. ISSN   0009-2665. PMID   18426241.
  17. ↑ Silva, A. Prasanna de; Moody, Thomas S.; Wright, Glenn D. (2009-11-16). "Fluorescent PET (Photoinduced Electron Transfer) sensors as potent analytical tools". Analyst. 134 (12): 2385–93. Bibcode:2009Ana...134.2385D. doi:10.1039/B912527M. ISSN   1364-5528. PMID   19918605.
  18. ↑ Cotruvo, Joseph A.; Aron, Allegra T.; Ramos-Torres, Karla M.; Chang, Christopher J. (2015-07-07). "Synthetic fluorescent probes for studying copper in biological systems". Chemical Society Reviews. 44 (13): 4400–4414. doi:10.1039/c4cs00346b. PMC   4478099 . PMID   25692243.
  19. ↑ Ashton, Trent D.; Jolliffe, Katrina A.; Pfeffer, Frederick M. (2015-07-07). "Luminescent probes for the bioimaging of small anionic species in vitro and in vivo". Chemical Society Reviews. 44 (14): 4547–4595. doi: 10.1039/C4CS00372A . hdl: 10536/DRO/DU:30076862 . ISSN   1460-4744. PMID   25673509.
  20. ↑ Poynton, Fergus E.; Bright, Sandra A.; Blasco, Salvador; Williams, D. Clive; Kelly, John M.; Gunnlaugsson, Thorfinnur (2017-12-11). "The development of ruthenium(II) polypyridyl complexes and conjugates for in vitro cellular and in vivo applications". Chemical Society Reviews. 46 (24): 7706–7756. doi:10.1039/C7CS00680B. ISSN   1460-4744. PMID   29177281. S2CID   4492751.
  21. ↑ Lin, Vivian S.; Chen, Wei; Xian, Ming; Chang, Christopher J. (2015-07-07). "Chemical probes for molecular imaging and detection of hydrogen sulfide and reactive sulfur species in biological systems". Chemical Society Reviews. 44 (14): 4596–4618. doi:10.1039/C4CS00298A. ISSN   1460-4744. PMC   4456340 . PMID   25474627.
  22. ↑ Hamilton, Graham R. C.; Sahoo, Suban K.; Kamila, Sukanta; Singh, Narinder; Kaur, Navneet; Hyland, Barry W.; Callan, John F. (2015-07-07). "Optical probes for the detection of protons, and alkali and alkaline earth metal cations". Chemical Society Reviews. 44 (13): 4415–4432. doi:10.1039/c4cs00365a. ISSN   1460-4744. PMID   25742963.
  23. ↑ Gale, Philip A.; Caltagirone, Claudia (2015-06-22). "Anion sensing by small molecules and molecular ensembles". Chemical Society Reviews. 44 (13): 4212–4227. doi:10.1039/C4CS00179F. ISSN   1460-4744. PMID   24975326.
  24. ↑ Gunnlaugsson, Thorfinnur; Glynn, Mark; Hussey), Gillian M. Tocci (née; Kruger, Paul E.; Pfeffer, Frederick M. (2006). "Anion recognition and sensing in organic and aqueous media using luminescent and colorimetric sensors". Coordination Chemistry Reviews. 250 (23–24): 3094–3117. doi:10.1016/j.ccr.2006.08.017.
  25. ↑ Anslyn, Eric V. (2007). "Supramolecular Analytical Chemistry". The Journal of Organic Chemistry. 72 (3): 687–699. doi:10.1021/jo0617971. PMID   17253783.
  26. 1 2 Huston, Michael E.; Akkaya, Engin U.; Czarnik, Anthony W. (1989-11-01). "Chelation enhanced fluorescence detection of non-metal ions". Journal of the American Chemical Society. 111 (23): 8735–8737. doi:10.1021/ja00205a034. ISSN   0002-7863.
  27. 1 2 Huston, Michael E.; Haider, Karl W.; Czarnik, Anthony W. (June 1988). "Chelation enhanced fluorescence in 9,10-bis[[(2-(dimethylamino)ethyl)methylamino]methyl]anthracene". Journal of the American Chemical Society. 110 (13): 4460–4462. doi:10.1021/ja00221a083. ISSN   0002-7863.
  28. 1 2 Akkaya, Engin U.; Huston, Michael E.; Czarnik, Anthony W. (1990-04-01). "Chelation-enhanced fluorescence of anthrylazamacrocycle conjugate probes in aqueous solution". Journal of the American Chemical Society. 112 (9): 3590–3593. doi:10.1021/ja00165a051. ISSN   0002-7863.
  29. 1 2 Silva, A. Prasanna de; Rupasinghe, R. A. D. Dayasiri (1985-01-01). "A new class of fluorescent pH indicators based on photo-induced electron transfer". Journal of the Chemical Society, Chemical Communications (23): 1669–1670. doi:10.1039/C39850001669. ISSN   0022-4936.
  30. 1 2 Silva, A. Prasanna de; Silva, Saliya A. de (1986-01-01). "Fluorescent signalling crown ethers; 'switching on' of fluorescence by alkali metal ion recognition and binding in situ". Journal of the Chemical Society, Chemical Communications (23): 1709–1710. doi:10.1039/C39860001709. ISSN   0022-4936.
  31. 1 2 Silva, A. Prasanna de; Gunaratne, H. Q. Nimal; Gunnlaugsson, Thorfinnur; Nieuwenhuizen, Mark (1996-01-01). "Fluorescent switches with high selectivity towards sodium ions: correlation of ion-induced conformation switching with fluorescence function". Chemical Communications (16): 1967. doi:10.1039/CC9960001967. ISSN   1364-548X.
  32. ↑ Minta, A.; Tsien, R. Y. (1989-11-15). "Fluorescent indicators for cytosolic sodium". The Journal of Biological Chemistry. 264 (32): 19449–19457. doi: 10.1016/S0021-9258(19)47321-3 . ISSN   0021-9258. PMID   2808435.
  33. ↑ Tsien, R. Y. (1989). "Chapter 5 Fluorescent Indicators of Ion Concentrations". Fluorescence Microscopy of Living Cells in Culture Part B. Quantitative Fluorescence Microscopy—Imaging and Spectroscopy. Methods in Cell Biology. Vol. 30. pp. 127–156. doi:10.1016/S0091-679X(08)60978-4. ISBN   9780125641302. ISSN   0091-679X. PMID   2538708.
  34. ↑ Minta, A.; Kao, J. P.; Tsien, R. Y. (1989-05-15). "Fluorescent indicators for cytosolic calcium based on rhodamine and fluorescein chromophores". The Journal of Biological Chemistry. 264 (14): 8171–8178. doi: 10.1016/S0021-9258(18)83165-9 . ISSN   0021-9258. PMID   2498308.
  35. ↑ Sousa, Lynn R.; Larson, James M. (1977-01-01). "Crown ether model systems for the study of photoexcited state response to geometrically oriented perturbers. The effect of alkali metal ions on emission from naphthalene derivatives". Journal of the American Chemical Society. 99 (1): 307–310. doi:10.1021/ja00443a084. ISSN   0002-7863.
  36. ↑ Konopelski, Joseph P.; Kotzyba-Hibert, Florence; Lehn, Jean-Marie; Desvergne, Jean-Pierre; Fagès, Frédéric; Castellan, Alain; Bouas-Laurent, Henri (1985-01-01). "Synthesis, cation binding, and photophysical properties of macrobicyclic anthraceno-cryptands". Journal of the Chemical Society, Chemical Communications (7): 433–436. doi:10.1039/C39850000433. ISSN   0022-4936.
  37. ↑ Fabbrizzi, Luigi; Poggi, Antonio (1995-01-01). "Sensors and switches from supramolecular chemistry". Chemical Society Reviews. 24 (3): 197. doi:10.1039/CS9952400197. ISSN   1460-4744.
  38. ↑ Devaraj, S.; Saravanakumar, D.; Kandaswamy, M. (2009-02-02). "Dual responsive chemosensors for anion and cation: Synthesis and studies of selective chemosensor for F− and Cu(II) ions". Sensors and Actuators B: Chemical. 136 (1): 13–19. doi:10.1016/j.snb.2008.11.018. ISSN   0925-4005.
  39. ↑ Calatrava-Pérez, Elena; Bright, Sandra A.; Achermann, Stefan; Moylan, Claire; Senge, Mathias O.; Veale, Emma B.; Williams, D. Clive; Gunnlaugsson, Thorfinnur; Scanlan, Eoin M. (2016-11-18). "Glycosidase activated release of fluorescent 1,8-naphthalimide probes for tumor cell imaging from glycosylated 'pro-probes'". Chemical Communications. 52 (89): 13086–13089. doi:10.1039/c6cc06451e. hdl: 2262/78923 . ISSN   1364-548X. PMID   27722254.
  40. ↑ Nguyen, Binh T.; Anslyn, Eric V. (2006-12-01). "Indicator–displacement assays". Coordination Chemistry Reviews. 250 (23–24): 3118–3127. doi:10.1016/j.ccr.2006.04.009. ISSN   0010-8545.
  41. ↑ Weller, A. (1968-01-01). "Electron-transfer and complex formation in the excited state". Pure and Applied Chemistry. 16 (1): 115–124. doi: 10.1351/pac196816010115 . ISSN   1365-3075. S2CID   54815825.
  42. ↑ Yoon, Juyoung; Czarnik, Anthony W. (1992-07-01). "Fluorescent chemosensors of carbohydrates. A means of chemically communicating the binding of polyols in water based on chelation-enhanced quenching". Journal of the American Chemical Society. 114 (14): 5874–5875. doi:10.1021/ja00040a067. ISSN   0002-7863.
  43. ↑ Gale, Philip A.; Caltagirone, Claudia (2018-01-01). "Fluorescent and colorimetric sensors for anionic species". Coordination Chemistry Reviews. 354: 2–27. doi:10.1016/j.ccr.2017.05.003. ISSN   0010-8545.
  44. ↑ Silvi, Serena; Credi, Alberto (2015-06-22). "Luminescent sensors based on quantum dot–molecule conjugates". Chemical Society Reviews. 44 (13): 4275–4289. doi:10.1039/C4CS00400K. hdl: 11585/521652 . ISSN   1460-4744. PMID   25912483.
  45. ↑ Baptista, Frederico R.; Belhout, S. A.; Giordani, S.; Quinn, S. J. (2015-06-22). "Recent developments in carbon nanomaterial sensors". Chemical Society Reviews. 44 (13): 4433–4453. doi:10.1039/C4CS00379A. hdl: 10197/11602 . ISSN   1460-4744. PMID   25980819.
  46. ↑ Wolfbeis, Otto S. (2015-07-07). "An overview of nanoparticles commonly used in fluorescent bioimaging". Chemical Society Reviews. 44 (14): 4743–4768. doi: 10.1039/C4CS00392F . ISSN   1460-4744. PMID   25620543.
  47. ↑ Taylor, Andrew J.; Hein, Robert; Patrick, Sophie C.; Davis, Jason J.; Beer, Paul D. (4 January 2024). "Anion Sensing through Redox-Modulated Fluorescent Halogen Bonding and Hydrogen Bonding Hosts**". Angewandte Chemie International Edition. 63 (6): e202315959. doi: 10.1002/anie.202315959 . PMID   38063409.
  48. ↑ Amoroso, Angelo J.; Pope, Simon J. A. (2015-07-07). "Using lanthanide ions in molecular bioimaging" (PDF). Chemical Society Reviews. 44 (14): 4723–4742. doi:10.1039/C4CS00293H. ISSN   1460-4744. PMID   25588358.
  49. ↑ Gunnlaugsson, Thorfinnur; Pope, Simon J.A. (2014). Luminescence of Lanthanide Ions in Coordination Compounds and Nanomaterials. Wiley-Blackwell. pp. 231–268. doi:10.1002/9781118682760.ch06. ISBN   9781118682760.
  50. ↑ Qin, Anjun; Tang, Ben Zhong, eds. (2013). Aggregation-Induced Emission: Fundamentals and Applications, Volumes 1 and 2. Wiley Online Books. doi:10.1002/9781118735183. ISBN   9781118735183.
  51. ↑ Hong, Yuning; Lam, Jacky W. Y.; Tang, Ben Zhong (2011-10-17). "Aggregation-induced emission". Chemical Society Reviews. 40 (11): 5361–88. doi:10.1039/c1cs15113d. ISSN   1460-4744. PMID   21799992. S2CID   6360212.
  52. ↑ Silva, A Prasanna de (2012-11-29). Molecular Logic-based Computation. Monographs in Supramolecular Chemistry. doi:10.1039/9781849733021. ISBN   9781849731485.
  53. ↑ Erbas-Cakmak, Sundus; Kolemen, Safacan; Sedgwick, Adam C.; Gunnlaugsson, Thorfinnur; James, Tony D.; Yoon, Juyoung; Akkaya, Engin U. (2018-04-03). "Molecular logic gates: the past, present and future". Chemical Society Reviews. 47 (7): 2228–2248. doi: 10.1039/C7CS00491E . hdl: 2262/91691 . ISSN   1460-4744. PMID   29493684.
  54. ↑ de Silva, Prasanna A.; Gunaratne, Nimal H. Q.; McCoy, Colin P. (July 1993). "A molecular photoionic AND gate based on fluorescent signalling". Nature. 364 (6432): 42–44. Bibcode:1993Natur.364...42D. doi:10.1038/364042a0. ISSN   1476-4687. S2CID   38260349.
This page is based on this Wikipedia article
Text is available under the CC BY-SA 4.0 license; additional terms may apply.
Images, videos and audio are available under their respective licenses.