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Background. The present work aims at formulating the melatonin-loaded nanoparticles (MTNPs) exhibiting the controlled-release and pH-sensitivity to repurpose the use of melatonin in the treatment of depressive-like behaviors and hypothalamus-pituitary-adrenal (HPA) axis dysregulation. Methods. MTNPs were characterized for the size, drug incorporation, and in vitro release in the different pH environments. Its merits were in vivo tested on the pinealectomized rats presenting the depressive-like behaviors and the abnormal HPA axis activity by calculating the improvement on saccharin preference, swimming immobility time, and the negative feedback of HPA axis. Results. Results revealed that MTNPs showed nanometer size, 15.77% of drug loading, 33.82% of encapsulation efficiency, the different controlled-release profiles in different pH environments (pH 1.2, pH 6.8, and pH 7.4), more sensitivity release in simulated intestinal fluid (pH 7.4) and blood (pH 6.8), and less sensitivity release in simulated gastric fluid (pH 1.2). Furthermore, MTNPs displayed better antidepressant actions in reducing the immobility time of forced swimming test, increasing the preference for saccharin, and sensitizing the blunt negative feedback of HPA axis, when compared to the free melatonin. Conclusions. The controlled-release nanoparticles is shown to be an effective improvement on the dosage form for melatonin, which is worthy of futuristic and complete evaluation. [ABSTRACT FROM AUTHOR]

Herein, we report a facile and label-free method for sensitive and specific determination of prostate cancer biomarker sarcosine via using photoluminescent bimetallic Au/Cu nanoplatelets (AuCu NPs) to construct an inner filter effect (IFE)-based photoluminescence (PL) sensing platform. The AuCu NPs were formed by the cysteine-induced co-reduction reaction, which displayed bright PL with an emission peak at 560 nm. Meanwhile, the Cu(I) doping caused a maximum 25-fold enhancement of quantum yield (QY), compared with the native Au(I) complexes, i.e., from 0.85 to 21.5%. By integrating the AuCu NPs with p-phenylenediamine (PPD) oxidation reaction, an IFE-based sensor for sarcosine detection was constructed. In this method, sarcosine is oxidized under the catalysis of sarcosine oxidase (SOx) to yield H 2 O 2. The latter further oxidizes PPD to form 2,5-diamino-N,N′-bis(p-aminophenyl)-l,4-benzoquinone di-imine (PPDox) in the presence of horseradish peroxidase (HRP). The UV–vis absorption spectrum of the PPDox can overlap well with the excitation and emission spectra of the AuCu NPs, resulting in the efficient quenching of the AuCu NPs via the IFE effect. Therefore, this IFE-based AuCu NPs/SOx/PPD/HRP sensing platform can be used for highly sensitive and specific sensing of sarcosine. The sensing platform showed two linear regions of the PL intensity of the AuCu NPs versus the concentration of sarcosine in the range of 0.5–5 μM and 5–100 μM with a detection limit (LOD) of 0.12 μM (S/N = 3). Furthermore, this IFE-based sensing platform could be developed into a paper-based biosensor for simple, instrument-free, and visual detection of sarcosine. Inner filter effect-based sensing platform for the detection of Sar. [Display omitted] • An inner filter effect-based photoluminescence sensing platform was constructed for sarcosine detection. • The quantum yield of the as-synthesized bimetallic Au/Cu nanoplatelets was up to 21.5%. • This is the first application of using photoluminescent bimetallic complexes for constructing an inner filter effect-based PL nanoprobe. [ABSTRACT FROM AUTHOR]

In biological systems, abnormal levels of hypochlorite (ClO−) could result in cell dysfunctions. Herein, we report a facile, one-step and green approach based on the versatile small biomolecule cysteine both serving as reducing agent and ligand for synthesizing the strongly photoluminencent and water-soluble Au(I)–Ag(I)-cysteine complexes nanoplatelets (Au(I)–Ag(I)-Cys nanoplatelets) for intracellular hypochlorite detection. Multiple spectroscopic and microscopical tools have been used to characterize the resultant Au(I)–Ag(I)-Cys nanoplatelets. It was found that with the cysteine-assisted synthesis approach, the Ag(I) doping to the Au(I) complexes could form the supramolecular organometallic nanoplatelets. Inside, the Au(I)–Ag(I) metallophilic interactions showing an Au to Ag charge transfer property were formed, thereby enhancing the photoluminescence (PL) intensity via the charge transfer from the bioligand's S to the metal-metal center. The quantum yield (QY) was measured to show a maximum 16-fold enhancement (i.e., from 0.85 to 13.8%). Interestingly, in the presence of ClO−, the metal-thiolate ligand structure of the as-synthesized Au(I)–Ag(I)-Cys nanoplatelets could be oxidatively damaged, causing the PL quenching, thereby producing the effect of biorecognition towards ClO− anions. The ClO−-induced PL quenching produced two linear regions at ClO− concentrations of 0.01–5.0 μM and 5.0–1000 μM with a limit of detection (LOD) of 8.0 nM (S/N = 3). The ClO−-induced PL quenching was specific over the other typical reactive oxygen species (ROS) and the potential interfering substances in biological samples. In addition, the Au(I)–Ag(I)-Cys nanoplatelets had good biocompatibility. Thus, they could be further developed as a biosensor for detecting endogenous ClO− anions in living cells. • Strongly photoluminencent and water-soluble Au(I)–Ag(I)-cysteine complexes nanoplatelets for intracellular hypochlorite detection is reported. • The quantum yield was measured to show a maximum 16-fold enhancement (i.e., from 0.85 to 13.8%), without the need of the treatment using additional organic solvents. • The as-synthesized Au(I)–Ag(I)-Cys nanoplatelets could be further developed as a biosensing platform for detecting endogenous ClO− anions in living cells. [ABSTRACT FROM AUTHOR]