A photoluminescence "switch-on" nanosensor composed of nitrogen and sulphur co-doped carbon dots and gold nanoparticles for discriminative detection of glutathione.

Biological thiols play a key role in biological processes and are involved in a variety of diseases. The discriminative detection of biological thiols is still challenging. In this contribution, a platform, an energy transfer-based quenching system composed of nitrogen and sulphur co-doped carbon dots (N, S-CDs) and gold nanoparticles (AuNPs), was established to discriminate glutathione (GSH) from other competitive biothiols including cysteine (Cys) and homocysteine (Hcy) based on a photoluminescence (PL) "switch-on" signal readout. The presence of GSH can encapsulate AuNPs in priority because of the strong affinity towards AuNPs and the steric hindrance effect of GSH, leaving little chance for the N, S-CDs binding on the surface of AuNPs and thus resulting in the PL recovery of N, S-CDs. Compared with the nitrogen-doped carbon dots (N-CDs), the N, S-CDs can enhance 10 times sensitivity for the designed PL "switch-on" sensing strategy. The proposed method has a detection limit of 3.6 nM and can be successfully applied for the detection of GSH in human serum.

Optically Active Ultrafine Au-Ag Alloy Nanoparticles Used for Colorimetric Chiral Recognition and Circular Dichroism Sensing of Enantiomers.

Despite a significant surge in the number of investigations into chirality at the nanoscale, especially thiolated chiral molecules capping gold clusters, only limited knowledge is currently available to elaborate the alloying effect on chiroptical behavior of bimetallic nanoparticles (NPs). Also, few successful cases as to the efforts toward the development of chirality-dependent applications on the optically active nanomaterial have been made. Herein, as a positive test case for chiral alloy nanoparticle synthesis, the stable and large chiroptical ultrafine Au-Ag alloy NPs were prepared by reduction of different molar fractions of HAuCl4 and AgNO3 with NaBH4 in the presence of d/l-penicillamine (d/l-Pen). Compared with those of monometallic Au and Ag counterparts with comparable size, the Au-Ag alloy NPs (Ag mole fraction, 70%) obviously displayed the largest optical activities with the maximum g-factors of ∼1.6 × 10-3. Impressively, the Pen-mediated synthesis of chiral Au-Ag alloy NPs possesses a colorimetric self-recognition function and can be used as an incisive circular dichroism (CD) probe toward d- and l-Pen enantiomers. The plasmonic CD signal amplification (ΔICD) shows good linearity with the amount of Pen over the range of 5.0-80.0 µM with a detection limit (3σ) of 1.7 µM for l-Pen and 1.5 µM for d-Pen, respectively. In addition, the sensing system exhibits good selectivity toward d- and l-Pen in the presence of other enantiomers; therefore, it is highly expected that the approach described here would open new opportunities for design of more novel enantioselective analyses of important species related to biological processes.