Circular dichroism sensor based on cadmium sulfide quantum dots for chiral identification and detection of penicillamine

A smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor for visual detection of mercury ions and l-penicillamine

Establishment of a rapid, sensitive, visual, accurate and low-cost fluorescence detection system to detect multiple targets was of great significance in food safety evaluation, ecological environment monitoring and human health monitoring. In this work, a smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor was proposed based on metal-organic framework (NH₂-MIL-101(Fe)) and CdTe quantum dots (CdTe QDs) for visual detection of mercury ions (Hg²⁺) and L-penicillamine (L-PA), in which NH₂-MIL-101(Fe) was used as the reference signal and CdTe QDs was used as the response signal. The down-conversion fluorescence system at excitation wavelength of 300 nm (ex: 330 nm) was used to detect Hg²⁺ and L-PA, in which the detection limit of Hg²⁺ was 0.053 nM with the fluorescence color changed from green to blue, and the detection limit of L-PA was 1.10 nM with the fluorescence color changed from blue to green. Meanwhile, the up-conversion fluorescence system at excitation wavelength of 700 nm (ex: 700 nm) was used to detect Hg²⁺ and L-PA. The detection limits of Hg²⁺ and L-PA were 0.11 nM and 2.93 nM, respectively. The detection of Hg²⁺ and L-PA were also carried out based on the color extraction RGB values identified by the smartphone with a detection limit of 0.091 nM for Hg²⁺ and 8.97 nM for L-PA. In addition, the concentrations of Hg²⁺ and L-PA were evaluated by three-dimensional dynamic analysis in complex environments. The smartphone-assisted down/up-conversion dual-mode ratiometric fluorescence sensor system provides a new strategy for detection Hg²⁺ and L-PA in food safety evaluation, environmental monitoring and human health monitoring.

DNA-Immobilized Special Conformation Recognition of L-Penicillamine Using a Chiral Molecular Imprinting Technique

A new chiral molecularly imprinted polymer (MIP) sensor with dual recognition ability was developed for the highly selective separation of enantiomers with toxic side effects in drugs. The sensor contains double-stranded deoxyribonucleic acid (dsDNA) as the element that immobilizes the chiral molecular conformation: the dsDNA enables the imprinted cavities to match the three-dimensional structure and functional groups from the chiral molecule. By embedding the spatial orientation of dsDNA in MIPs, one can accurately capture and immobilize the molecular conformation, eliminating the influence of interfering analogues. Herein, L-penicillamine (L-Pen) was selected as the chiral template molecule and embedded into dsDNA to form dsDNA-L-Pen complex, which was then embedded into the MIPs by electropolymerization. After elution, the stereo-selective imprinted cavities were obtained. The ATATATATATAT-TATATATATATA base sequence showed a high affinity for the embedded L-Pen, which endowed the imprinted cavities with a larger number of sites and improved the selectivity toward Pen enantiomers. Under the optimal working conditions, the current response of the MIP/dsDNA sensor exhibited a positive linear relationship with the logarithm of the L-Pen concentration in the range of 3.0 × 10^-16 to 3.0 × 10^-13 mol/L, and the detection limit was 2.48 × 10^-16 mol/L. After the introduction of dsDNA into the MIP, the selectivity of the sensor toward D-Pen increased by 6.4 times, and the sensor was successfully applied in the analysis of L-Pen in penicillamine tablets.

Nanomaterials-enriched sensors for detection of chiral pharmaceuticals

Advancements in nanoscience and nanotechnology have opened new pathways to fabricate novel nanostructures with interesting properties that would be used for different applications. In this respect, nanostructures comprising chirality are one of the most rapidly developing research fields encompassing chemistry, physics and biology. Chirality, also known as mirror asymmetry, describes the geometrical property of an object that is not superimposable on its mirror image. This characteristic plays a crucial role because these identical forms of chiral species in pharmaceuticals or food additives may exhibit different effects on living organisms. Therefore, chiral analysis is an important field of modern chemical analysis in health-related industries that are reliant on the production of enantiomeric compounds involving pharmaceuticals. This review covers the recent advances dealing with the synthesis, design and advantageous analytical performance of nanomaterials-enriched sensors used for chiral pharmaceuticals. We conclude this review with the challenges existing in this research field and our perspectives on some potential strategies with cutting-edge approaches for the rational design of sensors for chiral pharmaceuticals. We expect this comprehensive review will inspire future studies in nanomaterials-enriched chiral sensors.

Structural changes in selected human proteins induced by exposure to quantum dots, their biological relevance and possible biomedical applications

Quantum dots (QDs) are semi-conductor luminescent nanocrystals usually of 2-10 nm diameter, attracting the significant attention in biomedical studies since emerged. Due to their unique optical and electronic properties, i.e. wide absorption spectra, narrow tunable emission bands or stable, bright photoluminescence, QDs seem to be ideally suited for multi-colour, simultaneous bioimaging and cellular labeling at the molecular level as new-generation probes. A highly reactive surface of QDs allows for conjugating them to biomolecules, what enables their direct binding to areas of interest inside or outside the cell for biosensing or targeted delivery. Particularly protein-QDs conjugates are current subjects of research, as features of QDs can be combined with protein specific functionalities and therefore used as a complex in variety of biomedical applications. It is known that QDs are able to interact with cells, organelles and macromolecules of the human body after administration. QDs are reported to cause changes at proteins level, including unfolding and three-dimensional structure alterations which might hamper proteins from performing their physiological functions and thereby limit the use of QD-protein conjugates in vivo. Moreover, these changes may trigger unwanted cellular outcomes as the effect of different signaling pathways activation. In this review, characteristics of QDs interactions with certain human proteins are presented and discussed. Besides that, the following manuscript provides an overview on structural changes of specific proteins exposed to QDs and their biological and biomedical relevance.

Homochiral fluorescence responsive molecularly imprinted polymer: Highly chiral enantiomer resolution and quantitative detection of L-penicillamine

In this work, we innovatively synthesized homochiral fluorescence nano molecularly imprinted polymers (D-MIP) with dual affinity (metal ion affinity and homochiral affinity) for the specific separation and detection of L-penicillamine (L-PA), which is a core-shell structure with a SiO₂-covered CDs core and an imprinted layer with L-PA cavities. A switch for fluorescence response was built by chelating grafted Cu²⁺, what's more, the imprinted L-PA was pre immobilized by Cu²⁺ to form the directional imprinting with predetermined spatial structure. More importantly, the homochiral affinity of D-galactose in homochiral molecularly imprinted polymers (D-MIP) greatly enhanced the selective adsorption of L-PA, and D-MIP showed a high selectivity factor (α) of 3.45, which is 1.9 times that of the non-homochiral molecularly imprinted polymers (MIP). Meanwhile, D-MIP exhibited a high enantiomeric excess (ee) value of 56% for separation of racemic PA. Additionally, a high sensitive and selective method was established for the detection of L-PA.

Highly selective circular dichroism sensor based on d-penicillamine/cysteamine‑cadmium sulfide quantum dots for copper (II) ion detection

A highly selective circular dichroism sensor based on cysteamine-capped cadmium sulfide quantum dots (Cys-CdS QDs) was successfully developed for the determination of Cu²⁺. Basically, the Cys-CdS QDs are not active in circular dichroism spectroscopy. However, the circular dichroism probe (DPA@Cys-CdS QDs) can be simply generated in situ by mixing achiral Cys-CdS QDs with D-penicillamine. The detection principle was based on measuring the circular dichroism signal change upon the addition of Cu²⁺. The strong CD signal of the DPA@Cys-CdS QDs dramatically decreased in the presence of Cu²⁺, while other cations did not result in any spectral changes. In addition, the degree of the CD signal decrease was linearly proportional to the concentration of Cu²⁺ in the range of 0.50-2.25 μM (r² = 0.9919) with a detection limit of 0.34 μM. Furthermore, the proposed sensor was applied to detect Cu²⁺ in drinking water samples with %recovery values of 102-114% and %RSD less than 6%.

Nanoparticle-based Chemiluminescence for Chiral Discrimination of Thiol-Containing Amino Acids

The ability to recognize the molecular chirality of enantiomers is extremely important owing to their critical role in drug development and biochemistry. Convenient discrimination of enantiomers has remained a challenge due to lack of unsophisticated methods. In this work, we have reported a simple strategy for chiral recognition of thiol-containing amino acids including penicillamine (PA), and cysteine (Cys). We have successfully designed a nanoparticle-based chemiluminescence (CL) system based on the reaction between cadmium telluride quantum dots (CdTe QDs) and the enantiomers. The different interactions of CdTe QDs with PA enantiomers or Cys enantiomers led to different CL intensities, resulting in the chiral recognition of these enantiomers. The developed method showed the ability for determination of enantiomeric excess of PA and Cys. It has also obtained an enantioselective concentration range from 1.15 to 9.2 mM for PA. To demonstrate the potential application of this method, the designed platform was applied for the quantification of PA in urine and tablet samples. For the first time, we presented a novel practical application of nanoparticle-based CL system for chiral discrimination.

A circular dichroism sensor for selective detection of Cd2+ and S2- based on the in-situ generation of chiral CdS quantum dots

We demonstrate an advance in the fabrication of circular dichroism (CD) sensors for detection of Cd²⁺ and S^2- based on chiral CdS quantum dots (QDs) generated by a facile in-situ reaction. The chiral quantum dots are generated in solutions composed of Cd²⁺, S^2-, cysteamine (CA) and L-penicillamine (L-PA), with the number of the generated particles limited by either the Cd²⁺ or S^2- concentration. We show that the magnitude of the CD signal produced by the QDs is linearly related to the initial concentration of Cd²⁺ and S^2-, with excellent selectivity over other ions. Our sensor functions over concentration ranges of 65-200μM and 7-125μM with detection limits of 59.7 and 1.6μM for Cd²⁺ and S^2-, respectively. The sensor is applied in real water samples with results comparing favorably with those obtained from ICP-OES (for Cd²⁺) and HPLC (for S^2-).

Analysis of penicillamine using Cu-modified graphene quantum dots synthesized from uric acid as single precursor

A simple methodology was developed to quantify penicillamine (PA) in pharmaceutical samples, using the selective interaction of the drug with Cu-modified graphene quantum dots (Cu-GQDs). The proposed strategy combines the advantages of carbon dots (over other nanoparticles) with the high affinity of PA for the proposed Cu-GQDs, resulting in a significant and selective quenching effect. Under the optimum conditions for the interaction, a linear response (in the 0.10–7.50 µmol/L PA concentration range) was observed. The highly fluorescent GQDs used were synthesized using uric acid as single precursor and then characterized by high resolution transmission electron microscopy, Raman spectroscopy, X-ray diffraction, Fourier transform infrared spectroscopy, fluorescence, and absorption spectroscopy. The proposed methodology could also be extended to other compounds, further expanding the applicability of GQDs.

How to control optical activity in organic-silver hybrid nanoparticles

The mechanisms that originate and control optical activity in organic-metal hybrid nanoparticles (NPs) are identified using a time-perturbed density functional theory. Electronic circular dichroism (CD) is studied in terms of the intrinsic chirality of the ligands, the number of ligands and the induced chirality by the arrangement of the ligands on the NP. Left-handed cysteine and achiral methylthio ligands adsorbed on an icosahedral silver NP are investigated. The analysis of CD allows the identification of the spectral regions when the induced chirality by the ligand array dominates over the intrinsic chirality of the ligands, determining conditions for CD control and enlargement. These results would be significant in the discussion of experimental CD spectra of organic-metal hybrid NPs, which might allow the development of new strategies to improve the sensitivity of chiroptical spectroscopies for the identification of bio and organic molecules.