Single-Template Molecularly Imprinted Chiral Sensor for Simultaneous Recognition of Alanine and Tyrosine Enantiomers

A photothermal effect-based chiral sensor for chiral discrimination and sensitive detection

Chiral analysis with simple devices is of great importance for analytical chemistry. Based on the photothermal (PT) effect, a simple chiral sensor with a portable laser device as the light source and a thermometer as the detection tool was developed for the chiral recognition of tryptophan (Trp) isomers and the sensitive sensing of one isomer (L-Trp). Gold nanorods (GNRs), which have outstanding photo-thermal conversion ability due to their localized surface plasma resonance (LSPR) effect, are used as PT reagents, and biomacromolecules bovine serum albumin (BSA) are used as natural chiral sources, and thus, GNRs@BSA was obtained through Au-S bonds. The resultant GNRs@BSA displays higher affinity toward L-Trp than D-Trp owing to the inherent chirality of BSA. Under the irradiation of near-infrared (NIR) light, the temperature of GNRs@BSA//L-Trp is greatly lower than that of GNRs@BSA//D-Trp due to its greatly decreased thermal conductivity, and thus chiral discrimination of Trp isomers can be achieved. In addition, the developed PT effect-based chiral sensor can be used for sensitive detection of L-Trp, and the linear range and limit of detection (LOD) are 1 μM-10 mM and 0.43 μM, respectively.

Functionalized Chiral Materials for Use in Chiral Sensors

Chirality represents a fundamental attribute within living systems and is a pervasive phenomenon in the natural world. The identification and analysis of chiral materials within natural environments and biological systems hold paramount importance in clinical, chemical, and biological sciences. Within chiral analysis, there is a burgeoning focus on developing chiral sensors exhibiting exceptional selectivity, sensitivity, and stability, marking it as a forefront area of research. In the past decade (2013-2023), approximately 1990 papers concerning the application of various chiral materials in chiral sensors have been published. Biological materials and nanomaterials have important applications in the development of chiral sensors, which accounting for 26.67% and 45.24% of the material-related applications in these sensors, respectively; moreover, the development of chiral nanomaterials is closely related to the development of portable and stable chiral sensors. Natural chiral materials, utilized as selective recognition units, are combined with carriers characterized by good physical and chemical properties through functionalization to form various functional chiral materials, which improve the recognition efficiency of chiral sensors. In this article, from the perspective of biological materials, polymer materials, nanomaterials, and other functional chiral materials, the applications of chiral sensors are summarized and the research prospects of chiral sensors are discussed.

Colorimetric discrimination and spectroscopic detection of tyrosine enantiomers based on melamine induced aggregation of l-cysteine/Au nanoparticles

Au nanoparticles (AuNPs) are decorated by l-cysteine (L-Cys), and the resultant chiral L-Cys/AuNPs can be used for colorimetric discrimination and spectroscopic detection of the tyrosine (Tyr) enantiomers. Melamine (Mel) can induce the aggregation of the L-Cys/AuNPs through ligand exchange, leading to a distinct color change from wine red to purple. Owing to the same rotatory direction of L-Cys/AuNPs and L-Tyr, the L-Cys/AuNPs exhibit a significantly higher binding affinity toward L-Tyr than D-Tyr, and thus the Mel induced aggregation of the L-Cys/AuNPs is greatly alleviated by the protection from the L-Tyr protective layer. Therefore, the Tyr enantiomers can be simply discriminated by naked eyes. In addition, the absorbance of the aggregated L-Cys/AuNPs at ∼630 nm increases linearly with decreasing concentrations of L-Tyr ranging from 10 nM to 1 mM due to the weakened protection effect from L-Tyr, and thus spectroscopic detection of L-Tyr can also be accomplished by the developed L-Cys/AuNPs with a limit of detection (LOD) of 5.3 nM.

Monitoring levamisole in food and the environment with high selectivity using an electrochemical chiral sensor comprising an MOF and molecularly imprinted polymer

We used an enhanced recognition strategy to fabricate a novel levamisole-detecting chiral electrochemical sensor featuring a metal-organic framework (MOF) combined with a molecularly imprinted polymer (MIP). We first synthesised a Cu/Zn-[benzene-1,3,5-tricarboxylic acid] (Cu/Zn-BTC) MOF as the molecular immobilisation and signal-amplifying unit, and then prepared the MIP (molecular recognition unit) using levamisole as the template on a glassy carbon electrode modified with Cu/Zn-BTC. We obtained a composite chiral sensor with enhanced recognition capability for levamisole after template removal. Using the templated sites as the switch and K3[Fe(CN)6]/K4[Fe(CN)6] as a probe, we established a new method for detecting levamisole in meat products and water bodies. The linear detection range and detection limit of our chiral sensor are 5 to 6000 × 10-11 mol/L and 1.65 × 10-12 mol/L, respectively. Moreover, the sensor exhibited 93.8-109.0% recovery in the detection of levamisole in chicken and other real samples.

Chiral Confined Unimolecular Micelles for Controlled In Situ Fabrication of Optically Active Hybrid Nanostructures

Functional nanomaterials made by chiral induction have attracted extensive attention because of their intriguing characteristics and potential applications. However, the precise and controllable fabrication of chiral nanomaterials still remains challenging but is highly desired. In this study, chiral unimolecular micelles with different molecular weights and chiroptical activities were prepared by photoinduced atom transfer radical polymerization (photoATRP). Through nanoconfined growth, the chiral plasmonic nanoparticle assemblies with predesigned size and morphology were prepared using chiral unimolecular micelles as nanoreactors. The controllability over chiral assemblies and the size effect on chiroptical properties were also investigated. Furthermore, chiral complexes with absorption asymmetry and circularly polarized luminescence (glum = 4.25 × 10-4) were easily constructed via mixing of organic fluorescent molecules and chiral templates based on intermolecular hydrogen bonds. Such results indicated that our unimolecular-micelle-based templates enable the controllable preparation of both inorganic and organic chiral nanostructures with tailored dimensions, sizes, compositions, and optical activities.

Fluorescent/Colorimetric Dual-Mode Discriminating Gln and Val Enantiomers Based on Carbon Dots

Discrimination and quantification of amino acid (AA) enantiomers are particularly important for diagnosing and treating diseases. Recently, dual-mode probes have gained a lot of research interest because they can catch more detecting information compared with the single-mode probes. Thus, it is of great significance to develop a dual-mode sensor realizing AA enantiomer discrimination conveniently and efficiently. In this work, carbon dot L-TCDs were prepared by N-methyl-1,2-benzenediamine dihydrochloride (OTD) and l-tryptophan. With the assistance of H2O2, L-TCDs show an excellent discrimination performance for enantiomers of glutamine (Gln) and valine (Val) in both fluorescent and colorimetric modes. The fluorescence enantioselectivity of Gln (FD/FL) and Val (FL/FD) is 5.29 and 4.13, respectively, and the colorimetric enantioselectivity of Gln (ID/IL) and Val (IL/ID) is 13.26 and 3.42, individually. The chiral recognition mechanism of L-TCDs was systematically studied. L-TCDs can be etched by H2O2, and the participation of AA enantiomers results in different amounts of the released OTD, which provides fluorescent and colorimetric signals for identifying and quantifying the enantiomers of Gln and Val. This work provides a more convenient and flexible dual-mode sensing strategy for discriminating AA enantiomers, which is expected to be of great value in facile and high-throughput chiral recognition.

Chiral Materials: Progress, Applications, and Prospects

Chirality is a universal phenomenon in molecular and biological systems, denoting an asymmetric configurational property where an object cannot be superimposed onto its mirror image by any kind of translation or rotation, which is ubiquitous on the scale from neutrinos to spiral galaxies. Chirality plays a very important role in the life system. Many biological molecules in the life body show chirality, such as the "codebook" of the earth's biological diversity-DNA, nucleic acid, etc. Intriguingly, living organisms hierarchically consist of homochiral building blocks, for example, l-amino acids and d-sugars with unknown reason. When molecules with chirality interact with these chiral factors, only one conformation favors the positive development of life, that is, the chiral host environment can only selectively interact with chiral molecules of one of the conformations. The differences in chiral interactions are often manifested by chiral recognition, mutual matching, and interactions with chiral molecules, which means that the stereoselectivity of chiral molecules can produce changes in pharmacodynamics and pathology. Here, the latest investigations are summarized including the construction and applications of chiral materials based on natural small molecules as chiral source, natural biomacromolecules as chiral sources, and the material synthesized by design as a chiral source.

Novel graphene electrochemical transistors incorporating zirconia inorganic molecular imprinted layer：Design, construction and application for highly sensitive and selective detection of acetaminophen

Owing to their intrinsic amplifying effect together with chemical stability, graphene electrochemical transistor sensors (GECTs) are gaining momentum for sensing applications. However, the surface of GECTs for different detection substances must be modified with different recognition molecules, which was cumbersome and lack a universal method. Molecularly imprinted polymer (MIP) is a kind of polymer with specific recognition function for given molecules. Here, MIP and GECTs were combined to effectively solve the problem of weak selectivity of GECTs, and achieve the high sensitivity and selectivity of MIP-GECTs equipment in detecting acetaminophen (AP) in complex urine environment. A novel molecular imprinting sensor based on Au nanoparticles modified zirconia (ZrO₂) inorganic molecular imprinting membrane on reduced graphene oxide (ZrO₂-MIP-Au/rGO) was proposed. ZrO₂-MIP-Au/rGO was synthesized by one-step electropolymerization using AP as template, ZrO₂ precursor as the functional monomer. The -OH group on ZrO₂ and the -OH/-CONH- group on AP were easily bonded by hydrogen bonding to form a MIP layer on the surface, which allows the sensor to have a large number of imprinted cavities for AP specific adsorption. As a proof of method, the GECTs based on ZrO₂-MIP-Au/rGO functional gate electrode has the characteristics of wide linear range (0.1 nM-4 mM), low detection limit (0.1 nM) and high selectivity for AP detection. These achievements highlight the introduction of specific and selective MIP to GECTs with unique amplification function, which could effectively solve the problem of selectivity of GECTs in complex environments, suggesting the potential of MIP-GECTs in real-time diagnosis.

A surface molecularly imprinted electrochemical biosensor for the detection of SARS-CoV-2 spike protein by using Cu7S4-Au as built-in probe

Sensitive detection of severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) spike protein (S protein) is of significant clinical importance in the diagnosis of COVID-19 pandemic. In this work, a surface molecularly imprinted (SMI) electrochemical biosensor is fabricated for the detection of SARS-CoV-2 S protein. Cu₇S₄-Au is used as the built-in probe and modified on the surface of a screen-printed carbon electrode (SPCE). 4-Mercaptophenylboric acid (4-MPBA) is anchored to the surface of the Cu₇S₄-Au through Au-SH bonds, which can be used for the immobilization of the SARS-CoV-2 S protein template through boronate ester bonds. After that, 3-aminophenylboronic acid (3-APBA) is electropolymerized on the electrode surface and used as the molecularly imprinted polymers (MIPs). The SMI electrochemical biosensor is obtained after the elution of the SARS-CoV-2 S protein template with an acidic solution by the dissociation of the boronate ester bonds, which can be utilized for sensitive detection of the SARS-CoV-2 S protein. The developed SMI electrochemical biosensor displays high specificity, reproducibility and stability, which might be a potential and promising candidate for the clinical diagnosis of COVID-19.

Chiral molecular imprinting-based SERS detection strategy for absolute enantiomeric discrimination

Chiral discrimination is critical in environmental and life sciences. However, an ideal chiral discrimination strategy has not yet been developed because of the inevitable nonspecific binding entity of wrong enantiomers or insufficient intrinsic optical activities of chiral molecules. Here, we propose an "inspector" recognition mechanism (IRM), which is implemented on a chiral imprinted polydopamine (PDA) layer coated on surface-enhanced Raman scattering (SERS) tag layer. The IRM works based on the permeability change of the imprinted PDA after the chiral recognition and scrutiny of the permeability by an inspector molecule. Good enantiomer can specifically recognize and fully fill the chiral imprinted cavities, whereas the wrong cannot. Then a linear shape aminothiol molecule, as an inspector of the recognition status is introduced, which can only percolate through the vacant and nonspecifically occupied cavities, inducing the SERS signal to decrease. Accordingly, chirality information exclusively stems from good enantiomer specific binding, while nonspecific recognition of wrong enantiomer is curbed. The IRM benefits from sensitivity and versatility, enabling absolute discrimination of a wide variety of chiral molecules regardless of size, functional groups, polarities, optical activities, Raman scattering, and the number of chiral centers.

TiO2 Nanotubes Decorated with CdSe Quantum Dots: A Bifunctional Electrochemiluminescent Platform for Chiral Discrimination and Chiral Sensing

Chiral analysis is of significant importance for living organisms since chirality is the fundamental phenomenon in nature. In this work, a bifunctional electrochemiluminescent (ECL) platform is constructed for chiral discrimination and chiral sensing. 3-Mercaptopropionic acid-functionalized CdSe quantum dots (CdSe QDs) are combined with aminated TiO₂ nanotubes (NH₂-TiNTs) via amidation. The resultant CdSe QDs/TiNTs display significantly enhanced ECL signals due to the synergistic effect between CdSe QDs and TiNTs, which are then used for the chiral discrimination of the isomers of nine chiral amino acids (AAs) in the presence of d-AA oxidase (DAAO). DAAO can selectively catalyze the oxidation of d-AAs to generate H₂O₂, which acts as the coreaction reagent and triggers the ECL signals of CdSe QDs/TiNTs, and thus, the isomers of the nine chiral AAs can be effectively discriminated. In addition, the as-constructed ECL platform can also be used for the sensitive detection of d-AAs in the presence of DAAO with a wide linear range and a low limit of detection. These findings suggest that the CdSe QDs/TiNTs can work as a bifunctional ECL platform (chiral discrimination and chiral sensing), which might be an advanced ECL platform for biomedical applications.

Imprinted Electrochemical Sensor of Tyrosine Based on Chitosan/β- Cyclodextrin/Multi-walled Carbon Nanotubes Composite Film

Background:

As a vital amino acid in the human body, tyrosine is indispensable in various biological processes, and therefore its accurate and simple determination is of crucial importance. In this work, a facile approach was developed to construct a molecularly imprinted sensor for tyrosine via co-electrodeposition of chitosan, β-cyclodextrin and tyrosine on the surface of indium tin oxide that was pre-coated with multi-walled carbon nanotubes (MWNTs).

Methods:

Benefitting from the excellent film-forming ability and the rich functional groups to form a hydrogen bond with target molecules, chitosan was utilized to form a recognition matrix. MWNTs and β-cyclodextrin were then introduced to enhance the selectivity and sensitivity to tyrosine, due to the subtle electronic, catalytic properties and possible π-π interaction of MWNTs with tyrosine, as well as recognition ability of β-cyclodextrin. The morphology of the imprinted films was characterized by a scanning electron microscope. The electrochemistry and tyrosine sensing performance were investigated in detail by cyclic voltammetry and chronoamperometry.

Results:

Amperometry results showed that the imprinted sensor exhibited a linear range of 1.0×10−6 to 1.0×10−4 M and 1.0×10−4 to 1.0×10−3 M for tyrosine determination, with a detection limit of 6.0 × 10−7 M (S/N=3). Moreover, a satisfactory recovery in the range of 99.0% to 105.1% was obtained with the application of the imprinted sensor in artificial urine samples analysis.

Conclusion:

The imprinted electrode is reusable with satisfactory reproducibility and stability in tyrosine determination.

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.

Chiral nanomaterials for biosensing, bioimaging, and disease therapies

Chiral plasmonic nanomaterials for biosensing, bioimaging and disease therapy.

Doped Polythiophene Chiral Electrodes as Electrochemical Biosensors

π-conducting materials such as chiral polythiophenes exhibit excellent electrochemical stability in doped and undoped states on electrode surfaces (chiral electrodes), which help tune their physical and electronic properties for a wide range of uses. To overcome the limitations of traditional surface immobilization methods, an alternative pathway for the detection of organic and bioorganic targets using chiral electrodes has been developed. Moreover, chiral electrodes have the ability to carry functionalities, which helps the immobilization and recognition of bioorganic molecules. In this review, we describe the use of polythiophenes for the design of chiral electrodes and their applications as electrochemical biosensors.

Ultrasensitive Electrochemical Impedance Chiral Discrimination and Sensing of Tryptophan Isomers Based on Core-Shell-Structured Au-Ag Nanoparticles

Au-Ag nanoparticles (Au-Ag NPs) with a core-shell structure are prepared and used for ultrasensitive electrochemical impedance (EI) discrimination of the isomers of tryptophan (Trp). As revealed by circular dichroism, rotary polarization caused by the Au-Ag NPs is consistent with D-Trp but opposite to L-Trp, and thus, the Au-Ag NPs can selectively combine with D-Trp through preferential interactions. Compared with Au-Ag NPs, the composites of D-Trp and Au-Ag NPs (Au-Ag NPs/D-Trp) display significantly increased charge transfer resistance (R_ct); differently, the R_ct of Au-Ag NPs/L-Trp remains almost unchanged because the Au-Ag NPs exhibit poor affinity toward L-Trp. Therefore, ultrasensitive EI enantiodiscrimination of the isomers of Trp is realized even at an extremely low concentration of the Trp isomers (0.1 nM). In addition, it is successfully applied in the ultrasensitive determination of D-Trp at a low concentration level (0.1 nM∼10 μM).

Electrochemiluminescent chiral discrimination with chiral Ag2S quantum dots/few-layer carbon nitride nanosheets

Well-dispersed chiral Ag₂S quantum dots (Ag₂S QDs) were facilely synthesized by using N-acetyl-L-cysteine (NALC) as the chiral ligand and loaded onto nanosheets of two-dimensional (2D) few-layer carbon nitride (C₃N₄). The resultant nanocomposite (Ag₂S QDs/few-layer C₃N₄) shows enhanced electrochemiluminescence (ECL) while maintaining the chirality of Ag₂S QDs, which can be used for the chiral discrimination of the enantiomers of tyrosine (Tyr). Due to the higher affinity of chiral Ag₂S QDs toward L-Tyr than toward its enantiomer, the ECL intensity of Ag₂S QDs/few-layer C₃N₄ is significantly decreased after its incubation with L-Tyr, and thus the Tyr enantiomers can be discriminated. The developed ECL chiral sensor exhibits high stability and reproducibility. The universality of the ECL chiral sensor for the discrimination of other chiral amino acids is also studied, and the results indicate that it can work only in the case of chiral aromatic amino acids.

A biomolecule chiral interface base on BSA for electrochemical recognition of amine enantiomers

A composite chiral interface (BSA-MB-MWCNTs) was prepared from bovine serum albumin (BSA), methylene blue (MB), and multi-walled carbon nanotubes (MWCNTs) for chiral recognition of amine enantiomers (1S, 2S)-N,N'-dimethyl-1,2-cyclohexanediamine and (1R, 2R)-N,N'-dimethyl-1,2-cyclohexanediamine. The BSA-based composite was characterized by field emission scanning electron microscopy (FESEM) and ultraviolet-visible spectroscopy (UV-Vis). The electrochemical responses towards the two enantiomers were analyzed via cyclic voltammetry (CV), electrochemical AC impedance method (EIS), and differential-pulse voltammetry (DPV). The experimental results showed that the combination of MWCNTs and BSA could effectively improve the overall identification efficiency, and the peak current displayed by the S-enantiomer is larger, indicating that the prepared chiral surface has stronger interaction with the R-enantiomer. Under optimized condition, the current value of the oxidation peak of the chiral modified electrode showed a good linear relationship towards the amine concentration in the range of 5.0 × 10-3 to 5.0 × 10-5  mmol·L-1 . The proposed electrochemical chiral interface is easy to handle and provides a promising electrochemical sensing platform that can be used to identify chiral amine enantiomers.

Fluorometric discrimination of tyrosine isomers based on the inner filter effect of chiral Au nanoparticles on MoS2 quantum dots

A fluorescent chiral sensor is proposed based on the inner filter effect (IFE) of chiral Au nanoparticles (AuNPs) on MoS2 quantum dots (MoS2 QDs), which can be used for the discrimination of the isomers of tyrosine (Tyr). l-Tyrosine (l-Tyr) can induce obvious agglomeration of the chiral AuNPs, leading to an attenuated IFE of the chiral AuNPs and greatly restored fluorescence of the MoS2 QDs, and thus the enantioselective recognition of the Tyr isomers can be achieved. Also, l-Tyr but not d-Tyr induced agglomeration of the chiral AuNPs is confirmed by the larger association constant between l-Tyr and the chiral sensor.

Enantioselective recognition of tryptophan isomers with molecularly imprinted overoxidized polypyrrole/poly(p-aminobenzene sulfonic acid) modified electrode

Poly(p-aminobenzene sulfonic acid) (pABSA) was electrodeposited onto the surface of a glassy carbon electrode (GCE), which was then used for the preconcentration of l-tryptophan (l-Trp) due to the electrostatic and π-π interactions between pABSA and l-Trp. Polypyrrole (PPy) was electrodeposited onto the surface of the l-Trp enriched pABSA, and then the l-Trp templates were removed, resulting in molecularly imprinted PPy/pABSA. To avoid the interference from the oxidation peak of PPy on the following electrochemical chiral recognition of Trp isomers, PPy was overoxidized by cyclic voltammetry (CV). The resultant molecularly imprinted overoxidized PPy (OPPy)/pABSA modified GCE exhibits higher affinity toward l-Trp than d-tryptophan (d-Trp); that is, the oxidation peak current of l-Trp is greatly higher than that of d-Trp at the molecularly imprinted OPPy/pABSA modified GCE.

Silver nanoparticle driven signal amplification for electrochemical chiral discrimination of amino acids

β-Cyclodextrin (β-CD) modified silver nanoparticles (AgNPs), denoted as β-CD/AgNPs, were prepared by a simple one-pot method. Due to the inherent chirality of β-CD, the developed β-CD/AgNPs exhibited higher affinity toward l-tyrosine (l-Tyr) than d-tyrosine (d-Tyr), leading to serious aggregation of AgNPs in the presence of l-Tyr. Consequently, the l-Tyr induced aggregation of AgNPs can result in signal amplification in the differential pulse voltammograms (DPVs) of l-Tyr, which can be applied for the electrochemical chiral discrimination of the Tyr enantiomers. Other chiral amino acids including tryptophan and phenylalanine can also be successfully discriminated with the β-CD/AgNPs, suggesting high universality of the developed chiral sensor.

Colorimetric recognition of aromatic amino acid enantiomers by gluconic acid-capped gold nanoparticles

In this work, we prepared gold nanoparticles (AuNPs) by employing gluconic acid (GlcA) as reducing-cum-stabilizing agent. The proposed GlcA-AuNPs successfully worked as a colorimetric sensor for visual chiral recognition of aromatic amino acid enantiomers, namely tyrosine (D/L-Tyr), phenylalanine (D/L-Phe), and tryptophan (D/L-Trp). After adding L-types to GlcA-AuNPs solution, the color of the mixture changed from red to purple (or gray), while no obvious color change occurred on the addition of D-types. The effect can be detected by naked eyes. The particles have been characterized by transmission electron microscopy, Fourier-transform infrared spectroscopy, zeta potential, the dynamic light scattering analysis as well as UV-Vis spectroscopy. This assay can be used to determine the enantiomeric excess of L-Trp in the range from 0 to + 100%. The method has advantages in simplicity, sensitivity, fast response, and low cost.

Photoresponsive Surface Molecularly Imprinted Polymers for the Detection of Profenofos in Tomato and Mangosteen

As a moderately toxic organophosphorus pesticide, profenofos (PFF) is widely used in agricultural practice, resulting in the accumulation of a high amount of PFF in agricultural products and the environment. This will inevitably damage our health. Therefore, it is important to establish a convenient and sensitive method for the detection of PFF. This paper reports a photoresponsive surface-imprinted polymer based on poly(styrene-co-methyl acrylic acid) (PS-co-PMAA@PSMIPs) for the detection of PFF by using carboxyl-capped polystyrene microspheres (PS-co-PMAA), PFF, 4-((4-(methacryloyloxy)phenyl)diazenyl) benzoic acid, and triethanolamine trimethacrylate as the substrate, template, functional monomer, and cross-linker, respectively. PS-co-PMAA@PSMIP shows good photoresponsive properties in DMSO/H2O (3:1, v/v). Its photoisomerization rate constant exhibits a good linear relationship with PFF concentration in the range of 0~15 μmol/L. PS-co-PMAA@PSMIP was applied for the determination of PFF in spiked tomato and mangosteen with good recoveries ranging in 94.4-102.4%.

Hybrid carbon nanotubes modified glassy carbon electrode for selective, sensitive and simultaneous detection of dopamine and uric acid

Based on a hybrid carbon nanotube composite, a novel electrochemical sensor with high sensitivity and selectivity was designed for the simultaneous determination of dopamine (DA) and uric acid (UA). The hybrid carbon nanotube composite was prepared by ultrasonic assembly of carboxylated multi-walled carbon nanotube (MWCNT-COOH) and hydroxylated single-walled carbon nanotube (SWCNT-OH). And the hybrid (MWCNT-COOH/SWCNT-OH) composite was characterized by field emission scanning electron microscopy (FE-SEM) and Fourier transform infrared (FT-IR) spectroscopy. The electrochemical performances of MWCNT-COOH/SWCNT-OH composite modified glassy carbon electrode (MWCNT-COOH/SWCNT-OH/GCE) were analyzed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and differential pulse voltammetry (DPV). Under the optimum experimental conditions, the as-prepared sensor showed high sensitivity and selectivity for DA and UA. The calibration curves obtained were linear for the currents versus DA and UA concentrations in the range 2-150 μM, and limits of detection (LODs) were calculated to be 0.37 μM and 0.61 μM (signal-to-noise ratio of 3, S/N = 3), respectively. The recoveries of DA and UA in bovine serum samples at MWCNT-COOH/SWCNT-OH/GCE were in the range 96.18-105.02%, and relative standard deviations (RSDs) were 3.34-7.27%. The proposed electrochemical sensor showed good anti-interference ability, excellent reproducibility and stability, as well as high selectivity, which might provide a promising platform for determination of DA and UA.

Sensitive and selective detection of glycoprotein based on dual-signal and dual-recognition electrochemical sensing platform

Glycoproteins play extraordinary roles in biology and clinic. The specifically sensitive detection of glycoproteins by electrochemical methods is still a challenging task due to their poor electro-activity and sensitive nature to environment. In this work, ovalbumin (OVA), a model glycoprotein, was sensitively detected by a molecularly imprinted polymer (MIP) based electrochemical sensor, which was prepared by electropolymerizing 3-thiophene boric acid in the presence of OVA. Due to boronate affinity, the rebound OVA interacted with ferrocene boric acid (Fc-BA) to construct a sandwich structural sensing platform. Dual-recognition elements, imprinted effect and the boronate affinity, enabled the sensor to recognize OVA from other proteins. The rebinding of OVA caused the current changes of thionine and Fc-BA, which were combined as a dual-signal for OVA sensitive detection with a low limit of detection of 0.82 pg/mL (S/N = 3). The good performances of sensor indicated its potential applications in clinical diagnosis and other related fields.

Visual chiral recognition of aromatic amino acids with (S)-mandelic acid-based ionic liquids via complexation

Recently, chiral ionic liquids have attracted increasing attention in analytical chemistry. However, only a few papers focus on the application of them in visual chiral recognition. Herein, two functionalized chiral ionic liquids derived from (S)-mandelic acid (1-butyl-3-methylimidazolium mandelate, CIL1 and N-butyl-N-methylpyrrolidinium mandelate, CIL2) were prepared for visual chiral recognition of aromatic amino acids for the first time. In the presence of Cu(II) and appropriate solvents, visual enantiomeric responses of phenylalanine, tryptophane, tyrosine and phenylglycine were observed. Relying on solubility or color differences, all chiral recognition could be finished within 5 min. The potential mechanism was investigated by means of infrared spectroscopy, ultraviolet spectroscopy, thermal gravity analysis, elemental analysis and scanning electron microscope. Results revealed that CuSO₄ interacted with CIL1 and D-tryptophane in the ratio of 1:1.96:0.43 in relevant precipitate, and the different stability of complex was responsible for the chiral recognition. In addition, resolution of racemic tryptophane was performed, which offered excellent enantiomeric excess values (94.2% for CIL1 and 95.1% for CIL2 in solid phase). The proposed ionic liquids had strong enantioselectivity for aromatic amino acids and great potential in visual chiral recognition.