Chiral recognition and quantitative analysis of tyrosine enantiomers using L-cysteine capped CdTe quantum dots: Circular dichroism, fluorescence, and theoretical calculation studies

Fluorescence and Circular Dichroism Dual-Mode Probe for Chiral Recognition of Tyrosine and Its Applications in Bioimaging

Chiral amino acids (AAs) are essential in metabolism and understanding physiological processes, and they could be used as biomarkers for the diagnosis of different diseases. In this study, chiral Cdots@Van were prepared by postmodifying an achiral Cdots core with vancomycin for recognizing and determining the enantiomeric excess (ee) of tyrosine (Tyr) enantiomers. The fluorescence response of Cdots@Van is based on an "on-off" strategy, with different quenching percentages for d- and l-tyrosine. Interestingly, the circular dichroism (CD) spectrum of Cdots@Van responded to only one form of Tyr enantiomer, specifically d-Tyr, and remained nearly unchanged upon the addition of l-Tyr. Quantum mechanical (QM) calculations were in excellent agreement with the experimental results, confirming the stronger binding affinity of Cdots@Van for d-Tyr compared to l-Tyr. We further investigated the chiral recognition ability of the interconnected vancomycin particles, which was synthesized using the EDC/NHS coupling reaction between vancomycin molecules without a Cdots core. Surprisingly, unlike free vancomycin molecules, interconnected vancomycin displayed an enantiomeric recognition ability by CD spectroscopy, similar to what was observed for Cdots@Van. Crucially, this chiral probe has been successfully utilized for cell imaging applications.

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.

Novel Chiral CsPbBr3 Metal Halide Perovskite Magic-Sized Clusters and Metal Halide Molecular Clusters with Achiral Ligands

We have synthesized inherently chiral cesium lead halide perovskite magic-sized clusters (PMSCs) and ligand-assisted metal halide molecular clusters (MHMCs) using the achiral ligands octanoic acid (OCA) and octylamine (OCAm). UV-vis electronic absorption was used to confirm characteristic absorption bands while circular dichroism (CD) spectroscopy was utilized to determine their chiroptical activity in the 412-419 and 395-405 nm regions, respectively. In contrast, the larger sized counterpart of PMSCs, namely, perovskite quantum dots (PQDs), do not show chirality. The inherent chirality of the clusters is tentatively attributed to a twisted chiral layered structure, defect-induced chiral structure, or twisted Pb-Br octahedra.

A cooperation tale of biomolecules and nanomaterials in nanoscale chiral sensing and separation

The cooperative relationship between biomolecules and nanomaterials makes up a beautiful tale about nanoscale chiral sensing and separation. Biomolecules are considered a fabulous chirality 'donor' to develop chiral sensors and separation systems. Nature has endowed biomolecules with mysterious chirality. Various nanomaterials with specific physicochemical attributes can realize the transmission and amplification of this chirality. We focus on highlighting the advantages of combining biomolecules and nanomaterials in nanoscale chirality. To enhance the sensors' detection sensitivity, novel cooperation approaches between nanomaterials and biomolecules have attracted tremendous attention. Moreover, innovative biomolecule-based nanocomposites possess great importance in developing chiral separation systems with improved assay performance. This review describes the formation of a network based on nanomaterials and biomolecules mainly including DNA, proteins, peptides, amino acids, and polysaccharides. We hope this tale will record the perpetual relation between biomolecules and nanomaterials in nanoscale chirality.

Aqueous synthesis of red fluorescent l-cysteine functionalized Cu2S quantum dots with potential application as an As(iii) aptasensor

Water-stable Cu2S quantum dots were obtained by applying l-cysteine as a Cu(ii) to Cu(i) reducer and stabilizer in water and using an inert atmosphere at ambient temperature. The obtained quantum dots were characterized by STEM, XRD, FT-IR, UV-Vis, Raman, and fluorescence spectroscopy. The synthesis was optimized to achieve Cu2S quantum dots with an average diameter of about 9 nm that show red fluorescence emission. l-cysteine stabilization mediates crystallite growth, avoids aggregation of the quantum dots, and allows water solubility through polar functional groups, improving the fluorescence. The fluorometric test in the presence of the aptamer showed a shift in fluorescence intensity when an aliquot of As(iii) with a concentration of 100 pmol l-1 is incorporated because As(iii) and the used aptamer make a complex, leaving free the quantum dots and recovering their fluorescence response. The developed Cu2S quantum dots open possibilities for fluorescent detection of different analytes by simply changing aptamers according to the analyte to be detected.

Effective enantioselective recognition by steady-state fluorescence spectroscopy: Towards a paradigm shift to optical sensors with unusual chemical architecture

A series of amino acid-derived 1,2,3-triazoles presenting the amino acid residue and the benzazole fluorophore connected by a triazole-4-carboxylate spacer was studied for enantioselective recognition using only steady-state fluorescence spectroscopy in solution. In this investigation, the optical sensing was performed with D-(-) and L-(+)-Arabinose and (R)-(-) and (S)-(+)-Mandelic acid as chiral analytes. The optical sensors showed specific interactions with each pair of enantiomers, allowing photophysical responses, which were used for their enantioselective recognition. DFT calculations confirm the specific interaction between the fluorophores and the analytes corroborating the observed high enantioselectivity of these compounds with the studied enantiomers. Finally, this study investigated nontrivial sensors for chiral molecules by a mechanism different than turn-on fluorescence and has the potential to broad chiral compounds with fluorophoric units as optical sensors for enantioselective sensing.

Chiral inorganic nanomaterials for biological applications

Chiral nanomaterials in biology play indispensable roles in maintaining numerous physiological processes, such as signaling, site-specific catalysis, transport, protection, and synthesis. Like natural chiral nanomaterials, chiral inorganic nanomaterials can also be established with similar size, charge, surface properties, and morphology. However, chiral inorganic nanomaterials usually exhibit extraordinary properties that are different from those of organic materials, such as high g-factor values, broad distribution range, and symmetrical mirror configurations. Because of these unique characteristics, there is great potential for application in the fields of biosensing, drug delivery, early diagnosis, bio-imaging, and disease therapy. Related research is summarized and discussed in this review to showcase the bio-functions and bio-applications of chiral inorganic nanomaterials, including the construction methods, classification and properties, and biological applications of chiral inorganic nanomaterials. Moreover, the deficiencies in existing studies are noted, and future development is prospected. This review will provide helpful guidance for constructing chiral inorganic nanomaterials with specific bio-functions for problem solving in living systems.

A high-performance SERS imprinted membrane based on Ag/CNTs for selective detection of spiramycin

In this test, the eggshell membrane (ESM) is selected as the support membrane for the biocompatibility and anchors CNTs on the surface to increase the mechanical properties. Then Ag NPs are decorated on CNTs-ESM substrate as SERS substrate by twice in-situ reduction. Finally, a layer of imprinted polymers is coated on the surface of the substrate to synthesize the imprinted membrane for selective detection of spiramycin. It is exhibited from the characteristic results that the CNTs significantly increase the mechanical properties and the detection sensitivity, simultaneously. When the concentration of SP changes between 10^-6 ∼ 10^-11 M, there is a linear relationship between SERS intensity and SP concentration. The detection limit is 10^-11 M, and the correlation coefficient R² is 0.9864. The SERS imprinted membrane can be applied into the detection of antibiotics in practical sample, which broadens the research field of antibiotics detection.

Boosting chiral amplification in plasmon-coupled circular dichroism using discrete silver nanorods as amplifiers

Remarkable chiral amplification in plasmon-coupled circular dichroism spectroscopy (CD) is demonstrated by using discrete Ag nanorods as amplifiers. An unprecedented CD enhancement factor of over 3000 times is achieved without resonant or near-resonant exciton-plasmon couplings.

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.

Optical nanoprobes for chiral discrimination

Chiral recognition can be achieved by exploiting chiral properties of nanoparticles within various colorimetric and luminescent sensing systems.