Enantioselective Sensors Research Articles

Design of Self-Standing Chiral Covalent-Organic Framework Nanochannel Membrane for Enantioselective Sensing.

Nanochannel membranes are promising materials for enantioselective sensing. However, it is difficult to make a compromise between the selectivity and permeability in traditional nanochannel membranes. Therefore, new types of nanochannel membranes with high enantioselectivity and excellent permeability should be explored for chiral analysis. Here, asymmetric catalysis strategy is reported for interfacial polymerization synthesis of chiral covalent-organic framework (cCOF) nanochannel membrane for enantioselective sensing. Chiral phenylethylamine (S/R-PEA) and 2,4,6-triformylphloroglucinol (TP) are used to prepare chiral TP monomer. 4,4',4″-triaminotriphenylamine (TAPA) is then condensed with chiral TP to obtain cCOF nanochannel membrane via a C═N Schiff-base reaction. The molar ratio of TP to S/R-PEA is adjusted so that S/R-PEA is bound to the aldehyde only or both the aldehyde and hydroxyl groups on TP to obtain chiral-induced COF (cCOF-1) or both chiral-induced and modified COF (cCOF-2) nanochannel membrane, respectively. The prepared cCOF-2 nanochannel membrane showed two times more selectivity for limonene enantiomers than cCOF-1 nanochannel membrane. Furthermore, cCOF-2 nanochannel platform exhibited excellent sensing performance for other chiral molecules such as limonene, propanediol, methylbutyric acid, ibuprofen, and naproxen (limits of detection of 19-42ngL-1, enantiomer excess of 63.6-86.3%). This work provides a promising way to develop cCOF-based nanochannel enantioselective sensor.

Remote magnetically stimulated xanthan-biochar-Fe3O4-molecularly imprinted biopolymer hydrogel toward electrochemical enantioselection of l-tryptophan

Monitoring the levels of L-Tryptophan (L-Trp) in body fluids is crucial due to its significant role in metabolism and protein synthesis, which ultimately affects neurological health. Herein, we have developed a novel magneto-responsive electrochemical enantioselective sensor for the recognition of L-Trp based on oriented biochar derived from Loofah, Fe3O4 nanoparticles, and molecularly imprinted polydopamine (MIPDA) in xanthan hydrogel. The successful synthesis of these materials has been confirmed through physicochemical and electrochemical characterization. Various operational factors such as pH, response time, loading sample volume, and loading of active materials were optimized. As a result, the sensor exhibited an affordable linear range of 1.0–60.0 μM, with a desirable limit of detection of 0.44 μM. Furthermore, the proposed electrochemical sensor demonstrated good reproducibility and desirable selectivity for the determination of L-Trp, making it suitable for analyzing L-Trp levels in human plasma and serum samples. The development presented offers an appealing, easily accessible, and efficient strategy. It utilizes xanthan hydrogel to improve mass transfer and adhesion, biochar-stabilized Fe3O4 to facilitate magnetic orientation and accelerate mass transfer and sensitivity, and polydopamine MIP to enhance selectivity. This approach enables on-site evaluation of L-Trp levels, which holds significant value for healthcare monitoring and early detection of related conditions.

Propranolol chiral analysis using voltammetric sensor based on triterpenoid-graphene oxide hybrid material

Enantioselective sensors are potentially in demand at all stages of the production, storage and use of drugs, including identifying impurities of undesirable isomers and improving stereoselective synthesis methods. A key aspect for enantioselective sensors design is the development of appropriate molecular architectures that make it possible to create recognition sites with different affinities for enantiomers. This experimental work proposes a new chiral sensor based on glassy carbon electrode (GCE) modified by graphene oxide (GO) covalent functionalized with pentacyclic triterpenoid betulonic acid (BetA) for voltammetric recognition and determination of propranolol (Prop) enantiomers. Characterization of the materials was carried out using FTIR spectroscopy, scanning electron microscopy and cyclic voltammetry. Differential pulse voltammetry was used for Prop enantiomers recognition and quantification. The potential difference reached 30 mV along with enanitoselectivity coefficient ipS/ipR equal to 1.30. The calculated binding energy for S-Prop/GO-BetA complex is higher by 4.801 kcal moll−1 compared to R-Prop/GO-BetA indicating a more favorable mutual arrangement of molecules. The linear determination range was established as 5.0 × 10-6 ∼ 1.0 × 10-4 mol·L-1 and 1.0 × 10-4 ∼ 4.0 × 10-4 mol·L-1 for both enantiomers. The detection limits were determined to be 3.9⋅10-7 mol·L-1 and 5.0⋅10-7 mol·L-1 for S-Prop and R-Prop, respectively. The standard spike-recovery tests were carried out in human biological fluids with recoveries 97.3 % − 106.9 % for both enantiomers. The proposed sensor was used to determine the ratio of Prop enantiomers in mixture by regression analysis with projection to latent structures (PLS). The purpose was to build a PLS-model based on a calibration set containing a known number of Prop enantiomers and recognize a test set prepared independently. All samples of test set are correctly identified and the RSD did not exceed 8.7 %. GCE modified by covalent functionalized GO with BetA showed better stability compared with noncovalent functionalization in terms of electrode degradation.

Chiral porphyrin-SiO2 nano helices-based sensors for vapor enantiomers recognition.

The ability of olfaction to distinguish odors is based on many different properties deriving from the molecular structure, including chirality. Even if the electronic nose (e-nose) concept has been widely used in strict analogy with biological systems to implement sensor arrays that recognize and distinguish complex odor matrices, the fabrication of an enantioselective e-nose remains a challenge. This paper introduces an array of quartz microbalances (QMB) functionalized with sensitive materials made of a combination of achiral receptors and silica nanohelices grafted by chiral and achiral porphyrins. In this combination, nanohelices provide a chiral template for the spatial arrangement of porphyrins, while porphyrins act as receptors that can interact differently with analytes. Remarkably, even if single sensors show scarce enantioselectivity, the signals of the overall array achieve recognition of the chiral identity of the five diverse enantiomeric pairs tested when the data are processed with proper multivariate algorithms. Such an innovative and generalizable approach is expected to enable the formation of an extensive library of readily integrable chiral receptors in enantioselective sensor arrays, potentially revolutionizing diverse fields such as agrochemicals, medicine, and environmental sciences.

Enantioanalysis of Serine Using Stochastic Enantioselective Sensors

Enantioanalysis of serine can act as a key factor for metabolomics of colon cancer. Therefore, two stochastic enantioselective sensors based on nanographene and copper oxide modified with calix[6]arene and calix[4]arene-25,26,27,28-tetrol have been designed, characterised and validated. High sensitivities, selectivities, and enantioselectivities were recorded for the enantioanalysis of serine at two pH values 7.40 and 3.00. At pH 7.40, for the L-serine the wider linear concentration range (1 × 10−17 − 1 × 10−2 mol l−1) was obtained using the sensor based on calix[4]arene-25,26,27,28-tetrol, while the best sensitivity (1.31 × 109 s−1 mol l−1) was given by the sensor based on calix[6]arene; for the assay of D-serine at the same pH the wider linear concentration range (1 × 10−18 − 1 × 10−2 mol l−1) and the higher sensitivity (3.78 × 1011 s−1 mol l−1) were obtained using the calix[4]arene-25,26,27,28-tetrol based sensor. At pH 3.00, for the assay of L-serine, the best sensitivity (3.75 × 107 s−1 mol l−1) was obtained using the sensor based on calix[4]arene-25,26,27,28-tetrol, while the wider linear concentration range (1 × 10−16 − 1 × 10−6 mol l−1) was obtained using the sensor based on calix[6]arene; a wider linear concentration range for the assay of D-serine (1 × 10−18 − 1 × 10−4 mol l−1) was given by the sensor based on calix[4]arene-25,26,27,28-tetrol, while for the same enantiomer the highest sensitivity (2.08 × 108 s−1 mol l−1) at this pH was obtained using the sensor based on calix[6]arene. The enantiomers of serine were able to be determined up to 1 × 10−18 mol l−1 with high recoveries, and low relative standard deviations.

Surface Topographical Engineering of Chiral Au Nanocrystals with Chiral Hot Spots for Plasmon-Enhanced Chiral Discrimination.

Surface roughness in chiral plasmonic nanostructures generates asymmetrical localized electromagnetic fields, which hold great promise for applications in chiral recognition, chiroptical spectroscopic sensing, and enantioselective photocatalysis. In this study, we develop a surface topographical engineering approach to precisely manipulate the surface structures of chiral Au nanocrystals. Through carefully controlling the amounts of l- or d-cystine (Cys) and the seed solution in the growth process, we successfully synthesize chiral Au nanocrystals with highly disordered, ordered, and less ordered wrinkled surfaces. An underlying principle governing the relationship between surface roughness, orderliness, and chiroptical response is also proposed. More importantly, the chiral ordered wrinkles on the surfaces of the nanocrystals generate asymmetrical localized electronic fields with enhanced intensity, which achieve excellent plasmon-enhanced chiral discrimination ability for penicillamine (Pen) enantiomers. This work offers exciting prospects for manipulating the surface structures of chiral nanocrystals and designing highly sensitive plasmon-enhanced enantioselective sensors with chiral hot spots.

All-plasmonic-metal chiral nanostructures fabricated by circularly polarized light

Chiral plasmonic nanostructures, which would be applied to enantioselective sensors and metasurfaces, can be prepared in an enantioselective manner by irradiation with circularly polarized light (CPL). However, their resonance sites have been covered with non-plasmonic, dielectric moieties. Here, we prepared all-silver chiral plasmonic nanostructures on a glass plate in one-step by irradiating 380–450 nm right- or left-CPL to an aqueous solution containing Ag+ and citrate ions. Achiral or racemic Ag nanoparticles with anisotropic geometry are deposited on a glass plate by photochemical electron transfer from citrate to Ag+ in the initial phase. The deposited nanoparticles are grown into chiral structures under CPL via generation of an electric field with chiral distributions. An achiral Ag nanoplate array was also grown under 600–700 nm CPL into chiral nanostructure arrays on the basis of hot electron reduction of Ag+.

Homochiral zeolites as chiral modifier for voltammetry sensors with high enantioselectivity

AbstractComposite enantioselective voltammetry sensors provide a well‐known solution for the analysis and discrimination of enantiomerical drugs by voltammetry. The design of such sensor presumes the use of chiral substances to impart chirality to the electrode surface. We present the results of applying a theoretical approach based on simulating the adsorption of analyte enantiomers for preparing high enantioselectivity of pioneering enantioselective sensors using homochiral zeolites as chiral modifiers.We investigated the ability of some homochiral zeolites like CZP, ITV, OSO, STW, MFI, and SOF to act as solid chiral modifiers. Using tryptophan and tyrosine as model objects, we found that the maximum difference between the adsorption energies (ΔEads) of enantiomers on zeolites occurs if enantiomers are placed into the pores of zeolites. The SOF zeolite demonstrates the best enantioselectivity to both amino acids. Moreover, we compared the theoretical results with the experimental enantioselectivity value for tryptophan on a sensor designed as a paste electrode with MFI as the chiral modifier. We found that the calculated value ΔEads(R‐S) = −11.0 kJ/mol for MFI, though it is not the best value in the zeolite set considered, it is still enough for the sensor with MFI as the chiral modifier to demonstrate a higher than usual enantioselectivity (ip1/ip2 = 1.58) in an experiment with R‐ and S‐ tryptophan as the analyte.

Metal–Organic Frameworks-Based Analytical Devices for Chiral Sensing and Separations: A Review (2012–2022)

Metal–organic frameworks (MOFs), as high-surface-area materials, have shown promise in various areas of application, such as chiral sensing and separation, due to their flexibility in design and organized porous cages. Researchers have been striving to design and develop high-performance enantiorecognition and separation analytical techniques in chiral science fields. The main aim of this review is to provide a comprehensive overview of chirality, state-of-the-art MOFs in chirality, and chiral analysis in the past decade, 2012–2022. The classification of this review includes chirality, principles of chiral analysis, the attraction of functional materials in chirality, MOFs in chiral analysis, MOFs for designing enantioselective sensors (fluorescence, circular dichroism, quartz crystal microbalance, electrochemical), and MOFs as chiral stationary phases (CSPs) for chromatographic enantioseparation (high-performance liquid chromatography, gas chromatography, and capillary electrochromatography). Finally, this review covers the vital progress of these materials with attention to the available opportunities and challenges in this topic.

Fabrication of nanostructured molecularly imprinted polymer as enantioselective sensor and sorbent for L-phenylalanine benzyl ester

Fabrication of nanostructured molecularly imprinted polymer as enantioselective sensor and sorbent for L-phenylalanine benzyl ester

Rational design of highly enantioselective composite voltammetric sensors using a computationally predicted chiral modifier.

The use of chiral modifiers is among the simplest and most popular strategies for synthesizing enantioselective voltammetric sensors that are applied for the analysis and discrimination of enantiomerical drugs in various media. The type and structure of the chiral modifier are the key factors for the creation of enantioselectivity to a specified analyte. We suggest a novel approach to the prediction of the quality of a chiral modifier for preparing highly enantioselective sensors. The suggested approach is based on the molecular mechanics modeling of the adsorption of analyte enantiomers on chiral modifiers and on the comparison of the corresponding adsorption energies (ΔEads ). The efficiency of our approach is demonstrated using the example of cyclodextrins and chiral single-wall carbon nanotubes as chiral modifiers, and a wide range of chiral analytes. We found that the experimental enantioselectivity (ϑexp ) measured using voltammetry linearly correlates with ΔEads . The suggested approach also showed good predictive power in application to enantioselective chromatography, which further validates its general applicability.

(Invited) Photoelectrochemical Fabrication of Chiral Plasmonic Nanostructures By Circularly Polarized Light

Chiral plasmonic nanostructures attracts attention because they are potentially applicable to optical materials such as enantioselective sensors and metamaterials, as well as photoelectrochemical devices. Chiral nanostructures are often prepared by electron beam lithography or synthesis based on DNA templates. We have recently developed a photoelectrochemical method, in which handedness of the chiral nanostructure can be controlled by right- or left- circularly polarized light.The photoelectrochemical method is based on plasmon-induced charge separation (PICS),1,2 in which electrons are injected from a plasmonic metal nanoparticle to a semiconductor such as titania in direct contact. In PICS, anodic reactions often occur at the resonance sites of the plasmonic nanoparticle, at which electron oscillation is localized.3,4 Energetic electron-hole pairs generate at the resonance site, and holes are used for the local anodic reaction, probably via trap sites. On the basis of the mechanisms, we have demonstrated site-selective etching of silver nanoparticles and site-selective deposition of lead oxide on gold nanoparticles.Under right-circularly polarized light (CPL), distribution of the resonance sites could be the mirror image of that under left-CPL.5 Therefore, we performed site-selective deposition of lead oxide on gold nanocuboids on titania under right- or left-CPL.6 As a result, lead oxide was deposited on the gold nanocuboids in a chiral geometry. The nanostructures thus obtained exhibited circular dichroism (CD), and the CD spectrum obtained for the structure prepared under right-CPL was opposite to that obtained for the structure prepared under left-CPL. Reversible switching of the handedness of the chiral plasmonic nanostructures can also be possible.7 This method also allows us to fabricate spiral nanostructures. 1. Y. Tian and T. Tatsuma, J. Am. Chem. Soc., 127, 7632 (2005). 2. T. Tatsuma, H. Nishi, and T. Ishida, Chem. Sci., 8, 3325 (2017) [review]. 3. I. Tanabe and T. Tatsuma, Nano Lett., 12, 5418 (2012). 4. T. Tatsuma and H. Nishi, Nanoscale Horiz., 5, 597 (2020) [review]. 5. S. Hashiyada, T. Narushima, and H. Okamoto, J. Phys. Chem. C, 118, 22229 (2014). 6. K. Saito and T. Tatsuma, Nano Lett., 18, 3209 (2018). 7. K. Morisawa, T. Ishida, and T. Tatsuma, ACS Nano, 14, 3603 (2020).

Fabrication of a "turn-on"-type enantioselective fluorescence sensor via a modified achiral MOF: applications for synchronous detection of phenylalaninol enantiomers.

Homochiral metal-organic frameworks (HMOFs) have garnered considerable attention due to their extrachiral properties and broad application for chiral recognition. However, assembling a pair of high-quality chiral MOFs for sensing enantiomers precisely is a formidable challenge because of the complicated chiral environment and uncontrollable coordinated conditions. Herein, one pair of homochiral UiO-66 analogues, S-1 (l-AP@UiO-66-(COOH)2) and R-1 (d-AP@UiO-66-(COOH)2), are reported for chiral recognition. They were fabricated via a condensation reaction between the carboxyl groups of UiO-66-(COOH)2 and amino groups of l/d-amino propanol (l/d-AP). These novel fluorescent probes exhibited highly enantioselective fluorescence enhancement towards l/d-phenylalaninol (l/d-PA). For example, when S-1 and R-1 were treated with l-PA or d-PA, they displayed different fluorescence responses: the enantiomeric fluorescence enhancement ratio (ef) was 2.51 and 0.41 for S-1 and R-1, respectively. Hence, a visible difference in fluorescence enhancement for l-PA and d-PA and excellent enantioselective behavior between S-1 and l-PA (or R-1 and d-PA) was displayed. Measurements of fluorescence lifetime, powder X-ray diffraction, molecular-dynamic simulations and Benesi-Hildebrand plots were employed to determine the observed high enantioselectivity for l/d-PA. In brief, we found that two post-modified HMOFs, S-1 and R-1, were outstanding enantioselective sensors for detecting l-PA and d-PA. They had a prominent difference in ef and remarkable enantioselectivity factor α and ΔΔG based on steric hindrance and stereochemical difference.

Electrochemical enantioselective sensor for effective recognition of tryptophan isomers based on chiral polyaniline twisted nanoribbon

Effective enantioselective recognition with chiral nanomaterials remains a challenge in the field of chemistry and biology. In this paper, a pair of left- and right-handed polyaniline (defined as S-PANI and R-PANI) were synthesized by chemical oxidation of aniline to form a specially twisted nanoribbon, which was induced by enantiomeric camphorsulfonic acid. Both S-PANI and R-PANI were used to construct electrochemical chiral sensors for the discrimination of tryptophan isomers (D- and L-Trp). Owing to the formation of efficient chiral nanospace with special nanoribbon morphology and enormous amounts of oxygen-containing functional groups of S-PANI or R-PANI, the high enantioselectivity was obtained with the recognition efficiency of 4.90 (D-Trp) on S-PANI and 4.20 (L-Trp) on R-PANI, respectively. The obtained chiral electrodes were also used for the determination of the enantiomeric excess (ee) for Trp, and a good linear relationship between peak currents and ee% of Trp was obtained. Furthermore, the strategy we proposed has tremendous potential in enantiomer recognition field.

Enantioselective Voltammetric Sensors on the Basis of Chiral Materials

The review presents exhaustive information for the last 5 years on the trends and methods of research, development, and application of enantioselective voltammetric sensors on the basis of new chiral materials for the recognition of enantiomers of biologically active and medicinal compounds. Enantioselective sensors on the basis of chiral Cu, Au, Ag, Pt, and Pd nanoparticles and single crystals, mesoporous metals with molecular imprints, single-wall carbon nanotubes, smart polymers, metal–organic frameworks and supramolecular assemblies, and chiral ionic liquids are considered. Examples of the recognition and determination of enantiomers in various samples and analytical characteristics of the proposed sensors are given. Problems and prospects of using enantioselective voltammetric sensors for the chiral recognition of optically active compounds are discussed.

Chiral single-walled carbon nanotubes as chiral selectors in multimode enantioselective sensors.

Single-walled carbon nanotube-(7,6) chirality was used for the design of multimode enantioselective sensors using different carbon matrices such as graphene paste, graphite paste, and carbon nanopowder-based paste. l- and d-malic acids were used as model analytes. The responses of the multimode sensors were evaluated for potentiometric and differential pulse voltammetry (DPV) modes. When carbon nanopowder was used as matrix, the multimode sensor was enantioselective for d-malic acid in the concentration range 10-3 to 10-15 mol/L for the potentiometric mode and 10-5 to 10-8 mol/L for the DPV mode. The graphite paste-based sensor was enantioselective for l-malic acid in the ranges: 10-10 to 10-13 for the potentiometric mode and 10-4 to 10-7 mol/L for the DPV mode. The sensors based on graphene and chiral single-walled carbon nanotubes were enantioselective for d-malic acid, and a response was obtained only in the DPV mode. Accordingly, the matrix influenced both the enantioselectivity and the sensitivity of the measurements. The application of the sensors was for the enantioanalysis of malic acid in wines and apple juice samples. The proposed method is fast and reliable and allows the quantification of l- and d-malic acids using electrochemical methods based on different principles, from the real samples after a buffering of the samples. The enantioanalysis of malic acid in wine and juice samples was performed with high recoveries (higher than 90.00%) and low relative standard deviation (RSD) (%) values (lower than 1.00%).

QCM based enantioselective discrimination of enantiomers by a pair of serine derived homochiral coordination polymers

Decoding enantioselective molecular interactions between sensors and guests into readable signal represents a great challenge in developing selective sensing technology. In this work, a pair of serine derivatives based homochiral coordination polymer (HCP) enantiomers, (L)-SA-Cd and (D)-SA-Cd, were synthesized and explored as enantioselective sensors towards guest enantiomers. Quartz crystal microbalance (QCM) technology was employed to indicate the gravimetric change of (L)- and (D)-SA-Cd towards variable chiral guests, and an enantioselective factor of 1.72 ± 0.15, 1.81 ± 0.08, 1.37 ± 0.03 and 2.89 ± 0.09 were achieved for lactic acid, menthol, valinol and 1-phenylethylamine (PEA), respectively. PEA was further selected to comprehensively study the enantioselectivity via electrochemical tests, HPLC analysis and theoretical calculations. By comparison with state-of-art works, the enantioselective discrimination for PEA enantiomers is better than a vast majority of similar reports. (L)- and (D)-form of SA-Cd exhibited mirror behaviors towards guest enantiomers, and control experiments indicated the role of HCP construction in enhancing enantioselectivity. H-bonding effect was found to be the binding force between SA-Cd and PEA, as verified by FT-IR and UV–Vis titration studies. Further DFT calculations revealed the existence of conformation oriented H-bonding between the chiral –OH groups of serine fragment and –NH2 group of PEA. The findings indicate that HCP construction represents an effective strategy for promoting enantioselectivity, and monitoring gravimetric change could be a promising general method in decoding most of the enantioselective recognition process.

Kissing interactions for the design of a multicolour fluorescence anisotropy chiral aptasensor

The development of enantioselective assays and sensors has received much attention for the determination of enantiomeric impurities. Herein, we demonstrated that the previously reported aptamer kissing complex (AKC) assay strategy can be implemented for designing a chiral tool that allows both the simultaneous enantiomer quantification and the enantiopurity analysis. D- and L-arginine vasopressin (AVP) were employed as model enantiomeric targets. The D- and L-AVP engineered aptamers (aptaswitch) were used as recognition units whereas the Fluorescein or Texas Red labelled D- and L-hairpin probes (aptakiss) served as probes of the enantiomer-dependent AKC formation. The orthogonal fluorescence anisotropy signaling scheme at two different emission wavelengths permitted the concomitant sensing of the AVP enantiomers in a single sample, under a high-throughput microplate format. It was also shown that the AKC-based enantioselective sensor allowed the enantiomeric impurity detection at a level as low as 0.01%.

Tailoring of photo-responsive molecularly imprinted polymers on multiwalled carbon nanotube as an enantioselective sensor and sorbent for L-PABE

The present work is aimed to the fabrication of enantioselective sorbent and sensor for the selective and specific recognition of L-phenylalanine benzyl ester (L-PABE) template molecule in photo-responsive molecularly imprinted polymer (PR-MIP). Here a photo-switchable azo-benzene derivative, 4-[(4-methacryloyloxy)phenylazo]benzoic acid (MPABA) is synthesised and used as the functional monomer. Composites of multiwalled carbon nanotubes (MWCNTs) and imprinted polymer were prepared using 1:4 mol imprinting ratio of L-PABE and MPABA and N,N-ethylene bismethacrylamide (EBMAA) as the crosslinking agent. Conventional bulk MIP and their respective non-imprinted polymers were also synthesised and characterized to investigate the influence of pre-organization of binding sites on the selectivity of L-PABE. The enantioselective sensor is fabricated on platinum working electrode using imprinted and non-imprinted polymers and their electrochemical measurements are investigated using cyclic voltammetry (CV), differential pulse voltammetry (DPV) and elctrochemical impendence spectroscopy (EIS). The platinum modified sensors possess a limit of detection and limit of quantification as 0.2086 μmol L−1 and 0.6953 μmol L−1 respectively. MWCNT-MIPs and MIPs exhibit the largest adsorption capacity towards L-PABE. The synthesised polymers reveal characteristic adsorption features and selectivity towards L-PABE in comparison with its enantiomer analogues. Photo-regulated uptake and release studies of MWCNT-MIP and MIP on L-PABE were also done to determine the photoswitching reversibility of functional monomer.

A chiral signal-amplified sensor for enantioselective discrimination of amino acids based on charge transfer-induced SERS.

An ultra-high sensitivity sensor with the function of chiral signal amplification has been proposed for the enantiomer discrimination of various amino acid enantiomers based on charge transfer (CT)-induced SERS spectroscopy. The introduced TiO2 in this sensor improves the CT behavior and discrimination efficiency distinctly and enantiomeric discrimination is realized even at low concentration.