A Color Sensor for Catecholamines

Recent Development on Sensing Strategies for Small Molecules Detections

Sensors play a critical role in the detection and monitoring of various substances present in our environment, providing us with valuable information about the world around us. Within the field of sensor development, one area that holds particular importance is the detection of small molecules. Small molecules encompass a wide range of organic or inorganic compounds with low molecular weight, typically below 900 Daltons including gases, volatile organic compounds, solvents, pesticides, drugs, biomarkers, toxins, and pollutants. The accurate and efficient detection of these small molecules has attracted significant interest from the scientific community due to its relevance in diverse fields such as environmental pollutants monitoring, medical diagnostics, industrial optimization, healthcare remedies, food safety, ecosystems, and aquatic and terrestrial life preservation. To meet the demand for precise and efficient monitoring of small molecules, this summary aims to provide an overview of recent advancements in sensing and quantification strategies for various organic small molecules including Hydrazine, Glucose, Morpholine, Ethanol amine, Nitrosamine, Oxygen, Nitro-aromatics, Phospholipids, Carbohydrates, Antibiotics, Pesticides, Drugs, Adenosine Triphosphate, Aromatic Amine, Glutathione, Hydrogen Peroxide, Acetone, Methyl Parathion, and Thiophenol. The focus is on understanding the receptor sensing mechanism, along with the electrical, optical, and electrochemical response. Additionally, the variations in UV-visible spectral properties of the ligands upon treatment with the receptor, fluorescence and absorption titration analysis for limit of detection (LOD) determination, and bioimaging analysis are discussed wherever applicable. It is anticipated that the information gathered from this literature survey will be helpful for the perusal of innovation regarding sensing strategies.

Synthesis of a Near-Infrared Fluorescent Probe for Imaging Catecholamines via a Tandem Nucleophilic Aromatic Substitution

A near-infrared (NIR) fluorescent probe NS667 was developed using a novel synthetic strategy by integrating an electron-rich 1,2,3,4-tetrahydroquinoxaline (THQ) into the scaffold from NS510, which binds to catecholamines with high affinity. The fluorophore core was constructed with a tandem nucleophilic aromatic substitution. Upon binding to catecholamines, the fluorescence of this probe shifted, with the emission in the NIR region. Live cell imaging results demonstrate that NS667 can effectively image norepinephrine in chromaffin cells with shifted fluorescence, which highlights the potential of the probe for neuroimaging in tissues.

Molecular Probes, Chemosensors, and Nanosensors for Optical Detection of Biorelevant Molecules and Ions in Aqueous Media and Biofluids

Synthetic molecular probes, chemosensors, and nanosensors used in combination with innovative assay protocols hold great potential for the development of robust, low-cost, and fast-responding sensors that are applicable in biofluids (urine, blood, and saliva). Particularly, the development of sensors for metabolites, neurotransmitters, drugs, and inorganic ions is highly desirable due to a lack of suitable biosensors. In addition, the monitoring and analysis of metabolic and signaling networks in cells and organisms by optical probes and chemosensors is becoming increasingly important in molecular biology and medicine. Thus, new perspectives for personalized diagnostics, theranostics, and biochemical/medical research will be unlocked when standing limitations of artificial binders and receptors are overcome. In this review, we survey synthetic sensing systems that have promising (future) application potential for the detection of small molecules, cations, and anions in aqueous media and biofluids. Special attention was given to sensing systems that provide a readily measurable optical signal through dynamic covalent chemistry, supramolecular host-guest interactions, or nanoparticles featuring plasmonic effects. This review shall also enable the reader to evaluate the current performance of molecular probes, chemosensors, and nanosensors in terms of sensitivity and selectivity with respect to practical requirement, and thereby inspiring new ideas for the development of further advanced systems.

Functionalized acupuncture needle as a SERS-active platform for rapid and sensitive determination of adenosine triphosphate

The development of sensitive and rapid methods for analysis and detection of small molecules is highly desirable for medical diagnostics and therapeutics. We report an acupuncture needle functionalized with gold nanoparticles (Au NPs) and a macrocyclic amine (MA) Raman tag as the platform to realize the sensitive detection of adenosine triphosphate (ATP) by surface-enhanced Raman spectroscopy (SERS). The assembled Au NPs with abundant hot spots on the surface of the needle avoids the aggregation of Au NPs and results in a good signal response. Moreover, there is strong combination between ATP and MA through electrostatic adsorption, hydrogen-bonding interactions, and π-π stacking, and as a consequence, this functionalized needle can be used as a SERS platform for detection of ATP (25 nM) through a decrease of the Raman signal of MA resulting from the high chemical affinity of ATP for MA. Specially, the Au NP/MA-functionalized needle is conveniently used to monitor ATP (100 nM) added to serum, and demonstrates great promise in the study and detection of ATP in a complex sample, laying the foundation for SERS applications in complex acupuncture specimens with fast response and simple operation. Graphical abstract.

A High-Affinity Fluorescent Sensor for Catecholamine: Application to Monitoring Norepinephrine Exocytosis

A fluorescent sensor for catecholamines, NS510, is presented. The sensor is based on a quinolone fluorophore incorporating a boronic acid recognition element that gives it high affinity for catecholamines and a turn-on response to norepinephrine. The sensor results in punctate staining of norepinephrine-enriched chromaffin cells visualized using confocal microscopy indicating that it stains the norepinephrine in secretory vesicles. Amperometry in conjunction with total internal reflection fluorescence (TIRF) microscopy demonstrates that the sensor can be used to observe destaining of individual chromaffin granules upon exocytosis. NS510 is the highest affinity fluorescent norepinephrine sensor currently available and can be used for measuring catecholamines in live-cell assays.

Synthesis and Evaluation of Protein-Phenylboronic Acid Conjugates as Lectin Mimetics

Glycan-binding molecules, such as lectins, are very important tools for characterizing, imaging, or targeting glycans and are often involved in either physiological or pathological processes. However, their availability is far less compared to the diversity of native glycans. Therefore, development of lectin mimetics with desired specificity and affinity is in high demand. Boronic acid reacts with 1,2- and 1,3-diols of saccharides in aqueous media through reversible boronate ester formation and are regarded as synthetic lectin mimetics. In this study, bovine serum albumin (BSA)-phenylboronic acid (PBA) conjugates were synthesized in a density-controlled manner by targeting both aspartic and glutamic acids to afford lectin mimetics with multivalent PBA, as multivalency is a key factor for glycan recognition in both specificity and affinity. The resultant BSA-PBA conjugates were characterized by sodium dodecyl sulfate polyacrylamide gel electrophoresis and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry analysis. Their macrophage cell surface glycan-binding capacity was characterized by a competitive lectin-binding assay examined by flow cytometry, and 3-(4,5-di-methylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay showed biocompatibility. These novel lectin mimetics will find a broad range of applications as they can be wittingly modified, altering binding specificity and capacity.

Catecholamine Detection Using a Functionalized Poly(l-dopa)-Coated Gate Field-Effect Transistor

A highly sensitive catecholamine (CA) sensor was created using a biointerface layer composed of a biopolymer and a potentiometric detection device. For the detection of CAs, 3-aminophenylboronic acid (3-NH₂-PBA) was reacted with the carboxyl side chain of l-3,4-dihydroxyphenylalanine (l-dopa, LD) and the PBA-modified l-dopa was directly copolymerized with LD on an Au electrode, resulting in a 3.5 nm thick PBA-modified poly(PBA-LD/LD) layer-coated Au electrode. By connecting the PBA-LD-coated Au electrode to a field-effect transistor (FET), the molecular charge changes at the biointerface of the Au electrode, which was caused by di-ester binding of the PBA-CA complex, were transduced into gate surface potential changes. Effective CAs included LD, dopamine (DA), norepinephrine (NE), and epinephrine (EP). The surface potential of the PBA-LD-coated Au changed after the addition of 40 nM of each CA solution; notably, the PBA-LD-coated Au showed a higher sensitivity to LD because the surface potential change could already be observed after 1 nM of LD was added. The fundamental parameter analyses of the PBA-LD to CA affinity from the surface potential shift against each CA concentration indicated the highest affinity to LD (binding constant (K_s): 1.68 × 10⁶ M^-1, maximum surface potential shift (V_max): 182 mV). Moreover, the limit of detection for each CA was 3.5 nM in LD, 12.0 nM in DA, 7.5 nM in NE, and 12.6 nM in EP. From these results, it is concluded that the poly(PBA-LD/LD)-coated gate FET could become a useful biosensor for neurotransmitters, hormones, and early detection of Parkinson's disease.

Chromogenic and Fluorogenic Probes for the Detection of Illicit Drugs

The consumption of illicit drugs has increased exponentially in recent years and has become a problem that worries both governments and international institutions. The rapid emergence of new compounds, their easy access, the low levels at which these substances are able to produce an effect, and their short time of permanence in the organism make it necessary to develop highly rapid, easy, sensitive, and selective methods for their detection. Currently, the most widely used methods for drug detection are based on techniques that require large measurement times, the use of sophisticated equipment, and qualified personnel. Chromo- and fluorogenic methods are an alternative to those classical procedures.

Colorimetric and fluorescent detection of hydrazine with high sensitivity and excellent selectivity

It is critical to develop probes for rapid, selective, and sensitive detection of the highly toxic hydrazine in both environmental and biological science. In this work, under mild condition, a novel colorimetric and off-on fluorescent probe was synthesized for rapid recognition of hydrazine with excellent selectivity over other various species including some biological species, metal ions and anions. The limit of quantification (LOQ) value was 1.5×10^-4M-3.2×10^-3M (colorimetric method) and 1.5×10^-4M-3.2×10^-3M (fluorescent method) with as low as detection limit of 46.2μM.

A new approach for turn-on fluorescence sensing of l-DOPA

Resa-Sulf, designed based on a redox reaction, was applied for turn-on fluorescence sensing and quantitative detection ofl-DOPA.

Nanomolar colorimetric quantitative detection of Fe³⁺ and PPi with high selectivity

A novel rhodamine and 8-hydroxyquinoline-based derivative was synthesized, which is shown to act as a colorimetric chemosensor for Fe(3+) in aqueous solution with high selectivity over various environmentally and biologically relevant metal ions and anions with a distinct color change from colorless to pink in very fast response time (<1 min). Fe(3+) can be detected quantitatively in the concentration range from 6.7 to 16 μM and the detection limit (LOD) on UV-vis response of the sensor can be as low as 15 nM. The 'in situ' prepared Fe(3+) complex (1⋅Fe) showed high selectivity toward PPi against many common anions, and sensitivity (the LOD can be as low as 71 nM). In addition, both the chemosensor and the 'in situ' prepared Fe(3+) complex are reusable for the detection of Fe(3+) and PPi respectively.

(13)C/(15)N-Enriched l-Dopa as a Triple-Resonance NMR Probe to Monitor Neurotransmitter Dopamine in the Brain and Liver Extracts of Mice

In an attempt to monitor μm-level trace constituents, we applied here (1)H-{(13)C-(15)N} triple-resonance nuclear magnetic resonance (NMR) to (13)C/(15)N-enriched l-Dopa as the inevitable precursor of the neurotransmitter dopamine in the brain. The perfect selectivity (to render endogenous components silent) and μm-level sensitivity (700 MHz spectrometer equipped with a cryogenic probe) of triple-resonance allowed the unambiguous and quantitative metabolic and pharmacokinetic analyses of administered l-Dopa/dopamine in the brain and liver of mice. The level of dopamine generated in the brain (within the range 7-76 μm, which covers the typical stimulated level of ∼30 μm) could be clearly monitored ex vivo, but was slightly short of the detection limit of a 7 T MR machine for small animals. This work suggests that μm-level trace constituents are potential targets of ex vivo monitoring as long as they contain N atom(s) and their appropriate (13)C/(15)N-enrichment is synthetically accessible.

Multicomponent covalent dye assembly for tight binding and sensitive sensing of l-DOPA

Exploitation of dye aggregation enables tight binding and sensitive sensing of bifunctional analyte l-DOPA, simply by mixing two monofunctional dyes.

Naked-eye-based selective detection of pyrophosphate with a Zn2+ complex in aqueous solution and electrospun nanofibers

Based on keto–enol transformation process, a zinc complex as a naked-eye-based chemosensor for pyrophosphate in aqueous solution and electrospun nanofibers has been developed.

Reagentless polyol detection by conductivity increase in the course of self-doping of boronate-substituted polyaniline

We report on the novel reagentless and label-free detection principle based on electroactive (conducting) polymers considering sensors for polyols, particularly, saccharides and hydroxy acids. Unlike the majority of impedimetric and conductometric (bio)sensors, which specific and unspecific signals are directed in the same way (resistance increase), making doubtful their real applications, the response of the reported system results in resistance decrease, which is directed oppositely to the background. The mechanism of the resistance decrease is the polyaniline self-doping, i.e., as an alternative to proton doping, an appearance of the negatively charged aromatic ring substituents in polymer chain. Negative charge "freezing" at the boron atom is indeed a result of complex formation with di- and polyols, specific binding. Changes in Raman spectra of boronate-substituted polyaniline after addition of glucose are similar to those caused by proton doping of the polymer. Thermodynamic data on interaction of the electropolymerized 3-aminophenylboronic acid with saccharides and hydroxy acids also confirm that the observed resistance decrease is due to polymer interaction with polyols. The first reported conductivity increase as a specific signal opens new horizons for reagentless affinity sensors, allowing the discrimination of specific affinity bindings from nonspecific interactions.

Quantitative multiplexing with nano-self-assemblies in SERS

Multiplexed or simultaneous detection of multiple analytes is a valuable tool in many analytical applications. However, complications caused by the presence of interfering compounds in a sample form a major drawback in existing molecular sensor technologies, particularly in multi-analyte systems. Although separating analytes through extraction or chromatography can partially address the problem of interferents, there remains a need for developing direct observational tools capable of multiplexing that can be applied in situ. Surface-enhanced Raman Spectroscopy (SERS) is an optical molecular finger-printing technique that has the ability to resolve analytes from within mixtures. SERS has attracted much attention for its potential in multiplexed sensing but it has been limited in its quantitative abilities. Here, we report a facile supramolecular SERS-based method for quantitative multiplex analysis of small organic molecules in aqueous environments such as human urine.

Design, synthesis and evaluation of a boronic acid based artificial receptor for (L)-DOPA in aqueous media

Design and synthesis of a boronic acid based artificial receptor which selectively and effectively bound to a neurotransmitter, l-DOPA (), in aqueous media. In addition, the synthetic receptor was found to effectively inhibit the DDC (l-DOPA decarboxylase) enzymatic reaction under physiological conditions.

Human dopamine receptor nanovesicles for gate-potential modulators in high-performance field-effect transistor biosensors

The development of molecular detection that allows rapid responses with high sensitivity and selectivity remains challenging. Herein, we demonstrate the strategy of novel bio-nanotechnology to successfully fabricate high-performance dopamine (DA) biosensor using DA Receptor-containing uniform-particle-shaped Nanovesicles-immobilized Carboxylated poly(3,4-ethylenedioxythiophene) (CPEDOT) NTs (DRNCNs). DA molecules are commonly associated with serious diseases, such as Parkinson's and Alzheimer's diseases. For the first time, nanovesicles containing a human DA receptor D1 (hDRD1) were successfully constructed from HEK-293 cells, stably expressing hDRD1. The nanovesicles containing hDRD1 as gate-potential modulator on the conducting polymer (CP) nanomaterial transistors provided high-performance responses to DA molecule owing to their uniform, monodispersive morphologies and outstanding discrimination ability. Specifically, the DRNCNs were integrated into a liquid-ion gated field-effect transistor (FET) system via immobilization and attachment processes, leading to high sensitivity and excellent selectivity toward DA in liquid state. Unprecedentedly, the minimum detectable level (MDL) from the field-induced DA responses was as low as 10 pM in real- time, which is 10 times more sensitive than that of previously reported CP based-DA biosensors. Moreover, the FET-type DRNCN biosensor had a rapid response time (<1 s) and showed excellent selectivity in human serum.

Supramolecular complexations of natural products

Complexations of natural products with synthetic receptors as well as the use of natural products as host compounds are reviewed, with an emphasis on possible practical uses or on biomedical significance. Applications such as separation, sensing, enzyme monitoring, and protection of natural drugs are first outlined. We then discuss examples of complexes with all important classes of natural compounds, such as amino acids, peptides, nucleosides/nucleotides, carbohydrates, catecholamines, flavonoids, terpenoids/steroids, alkaloids, antibiotics and toxins.

The effect of alkylation, protonation, and hydroxyl group substitution on reversible alcohol and water addition to 2- and 4-formyl pyridine derivatives

The regiochemical influence of hydroxyl or methoxy substitution on 2- and 4-formyl pyridine derivatives upon alcohol and water addition was studied.

Chemical sensing of neurotransmitters

This review focuses on the chemosensors for neurotransmitters published for the last 12 years, covering biogenic amines (dopamine, epinephrine, norepinephrine, serotonin, histamine and acetylcholine), amino acids (glutamate, aspartate, GABA, glycine and tyrosine), and adenosine.

Selective catecholamine recognition with NeuroSensor 521: a fluorescent sensor for the visualization of norepinephrine in fixed and live cells

A method for the selective labeling and imaging of catecholamines in live and fixed secretory cells is reported. The method integrates a tailored approach using a novel fluorescence-based turn-on molecular sensor (NeuroSensor 521) that can exploit the high concentration of neurotransmitters and acidic environment within secretory vesicles for the selective recognition of norepinephrine and dopamine. The utility of the method was demonstrated by selectively labeling and imaging norepinephrine in secretory vesicles such that discrimination between norepinephrine- and epinephrine-enriched populations of chromaffin cells was observed. This method was validated in fixed cells by co-staining with an anti-PNMT antibody.

Discrimination and classification of ginsenosides and ginsengs using bis-boronic acid receptors in dynamic multicomponent indicator displacement sensor arrays

Ginsenosides are complex natural products with a diverse array of biological activities, but their molecular recognition and sensing is challenging. A library of simple bis-boronic acid-based receptors with various spacers was synthesized for the sensing of ginsenosides. The incorporation of two boronic acids allowed the pairing of two indicators, which can simultaneously bind the receptors or two saccharides within the ginsenosides. A cross-reactive sensing array was therefore constructed using the receptors in conjunction with different pairs of indicators. LDA plots created from the colorimetric response of the hosts and indicator pairs reveal excellent classification of the ginsenosides, and the corresponding loading plots reveal the cross-reactivity of the receptors. In addition, several commercial ginseng extracts were unambiguously classified using the same sensing array. The assay reported here should be applicable to the analysis of other large saccharide-based natural products.

Using ratiometric indicator-displacement assays in semi-quantitative colorimetric determination of chloride, bromide, and iodide anions

A ratiometric indicator-displacement assay (RIDA) array has been developed for the semi-quantitative colorimetric determination of chloride, bromide, and iodide anions. Determinations of these halide anions follow the displacement reaction using the chelate compound of (2-(3,5-dibromo-2-pyridylazo)-5-(diethylamino)phenol) (3,5-Br2-PADAP) and heavy metal salts as colorimetric reagent. Different from regular silver nitrate titrations, the chloride, bromide, and iodide anions compete with the 3,5-Br2-PADAP ligand and change the colour of the 3,5-Br2-PADAP-metal chelate compound dramatically. These clearer colour changes make the semi-quantitative colorimetric determination of chloride, bromide, and iodide anions possible. The colour changes are imaged using a conventional flatbed scanner, and digitized. After statistical analysis, these colour changes in the RIDA array provide facile identification of chloride, bromide, and iodide anions at a wide concentration range (10 μM to 10 mM) without any misclassification. The RIDA array is able to discriminate without misclassifications among seven concentrations of chloride, bromide, and iodide anions. No shelf life issue exists because the chelating compounds react with halide anions directly without any pre-immobilizations.

A simple ionic triphenylene receptor for catecholamines, serotonin and D-glucosamine in buffered water

The combination of hydrophobic effects and ionic pairing within a triphenylene-based receptor were exploited for the binding of biological phenylethylamines, serotonin and D-glucosamine in phosphate buffered water.

Nanoscale polyoxometalate-based inorganic/organic hybrids

The latest advances in the area of polyoxometalate (POM)-based inorganic/organic hybrid materials prepared by self-assembly, covalent modification, and supramolecular interactions are presented. This Review is composed of five sections and documents the effect of organic cations on the formation of novel POMs, surfactant encapsulated POM-based hybrids, polymeric POM/organic hybrid materials, POMs-containing ionic crystals, and covalently functionalized POMs. In addition to their role in the charge-balancing, of anionic POMs, the crucial role of organic cations in the formation and functionalization of POM-based hybrid materials is discussed.

Molecular recognition of organic ammonium ions in solution using synthetic receptors

Ammonium ions are ubiquitous in chemistry and molecular biology. Considerable efforts have been undertaken to develop synthetic receptors for their selective molecular recognition. The type of host compounds for organic ammonium ion binding span a wide range from crown ethers to calixarenes to metal complexes. Typical intermolecular interactions are hydrogen bonds, electrostatic and cation-π interactions, hydrophobic interactions or reversible covalent bond formation. In this review we discuss the different classes of synthetic receptors for organic ammonium ion recognition and illustrate the scope and limitations of each class with selected examples from the recent literature. The molecular recognition of ammonium ions in amino acids is included and the enantioselective binding of chiral ammonium ions by synthetic receptors is also covered. In our conclusion we compare the strengths and weaknesses of the different types of ammonium ion receptors which may help to select the best approach for specific applications.

Carbohydrate recognition by boronolectins, small molecules, and lectins

Carbohydrates are known to mediate a large number of biological and pathological events. Small and macromolecules capable of carbohydrate recognition have great potentials as research tools, diagnostics, vectors for targeted delivery of therapeutic and imaging agents, and therapeutic agents. However, this potential is far from being realized. One key issue is the difficulty in the development of "binders" capable of specific recognition of carbohydrates of biological relevance. This review discusses systematically the general approaches that are available in developing carbohydrate sensors and "binders/receptors," and their applications. The focus is on discoveries during the last 5 years.

Application of a library of artificial receptors formed by the self-organization of N-lipidated peptides immobilized on cellulose in studying the effects of the incorporation of a fluorine atom

A library of artificial receptors formed by the self-organization of N-lipidated peptides attached to cellulose via m-aminophenylamino-1,3,5-triazine was used for docking pairs of small colorless N-phenylpiperazines with and without a fluorine atom in the phenyl ring. The interactions of guests with the receptors were visualized by using competitive adsorption-desorption of an appropriate reporter dye. Several library members demonstrated attributes characteristic of the detection of alterations in the guest structure caused by the substitution of one hydrogen atom with fluorine. Analysis of the binding pattern of N-phenylpiperazine derivatives showed two characteristic bonding patterns: one with stronger binding of fluorinated analogues and weaker binding of native phenyl substituted analogues by the most of the receptors studied and another one with stronger binding of native hydrogen substituted compounds and respectively weaker binding of fluorinated analogues of guest molecules by receptors with tryptophan inside the binding pocket.