Developing a label-free full-range highly selective pH nanobiosensor using a novel high quantum yield pH-responsive activated-protein-protected gold nanocluster prepared by a novel ultrasonication-protein-assisted procedure

A novel, label-free, ultra-selective, reproducible, and reversible pH nanobiosensor was developed for analyzing biofluids, food samples, and real water media utilizing a novel activated-protein-protected gold nanocluster with an ultra-narrow emission band, termed as ABSA-AuNCs. The ABSA-AuNCs were synthesized via a novel ultrasonication-protein-assisted procedure, for the first time, using activated bovine serum albumin as both capping and reducing agents. The ABSA-AuNCs revealed a highly narrow symmetric emission spectrum (λmax = 330.0 nm upon excitation at 312-317 nm), and a highly narrow size distribution of 2.9-3.7 nm along with an enhanced quantum yield of 28.3 %. At present, with a full width at half maximum (FWHM) of 14.0 nm, ABSA-AuNCs have the narrowest bandwidth of fluorescent nanomaterials reported to date. The ABSA-AuNCs were characterized for their stability, size, morphology, crystallinity, structural, and optical properties. The ABSA-AuNCs were found to be appropriate for constructing a label-free ultraselective pH nanobiosensor. A linear range over 2.0-11.0, fast response time of less than 5 s, and long-term stability of 99.7 % after 500 min were achieved. The %RSD for repeatability, intra-day reproducibility, and inter-day reproducibility was found to be 1.4 %, 1.7 %, and 2.3 %, in order, to reveal high repeatable and reproducible results. The selectivity of the pH biosensor was evaluated upon the addition of different interferents, indicating an excellent pH selectivity for the ABSA-AuNCs. Real sample analysis proved the feasibility of the ABSA-AuNCs for accurate, precise, and reliable pH sensing in biofluids (undiluted blood and urine), a variety of food samples, and several real water samples.

Developing a novel ultraselective and ultrasensitive label-free direct spectrofluorimetric nanobiosensor for direct highly fast field detection of explosive triacetone triperoxide

BACKGROUND

Direct detection of the notorious explosive triacetone triperoxide (TATP) is very difficult because it lacks facile ionization and UV absorbance or fluorescence. Besides, the current indirect methods are time-consuming and need a pre-step for TATP cleavage to hydrogen peroxide. Moreover, they commonly show significant false-positive results in the presence of some camouflage which limits their field applications. Herein, for the first time, a novel label-free field-applicable spectrofluorimetric nanobiosensor was developed for direct TATP detection using a novel activated-protein protected gold nanocluster (ABSA-AuNCs; QY = 28.3 %) synthesized by a combined protein-assisted-ultrasonication procedure.

RESULTS

The ABSA-AuNCs revealed a fluorescence spectrum centered at 330.0 nm which was significantly quenched by TATP (binding constant = 154.06 M-1; ΔG = -12.5 kJ mol-1; E(%) = 88.5 %). This phenomenon was used as a basis for direct TATP quantification, providing a working range of 0.01-40.0 mg L-1 and a detection limit of 6.7 μg L-1 which is the lowest LOD provided for TATP detection up to now. A %RSD of 0.9 % and 1.56 % was obtained for repeatability and inter-day reproducibility, respectively. The selectivity was checked against a variety of camouflages, revealing ultra-selectivity. Several synthetic samples prepared by several camouflages and real samples (clay soil and real water media) were analyzed, revealing quantitative recoveries of TATP.

SIGNIFICANCE

During the production of the notorious explosive TATP, it can be discharged into water and soil. This novel method eliminated the false-positive results of traditional methods and is applicable for direct quantitative detection of camouflaged TATP and its residues in real soil and water samples in a highly short response time (2 min). The camouflaged TATP analysis is important for tracking the terrorist attacks in field conditions and analysis of soil and water can provide a first indication of the location of the production site.

The Atomically Precise Gold/Captopril Nanocluster Au25(Capt)18 Gains Anticancer Activity by Inhibiting Mitochondrial Oxidative Phosphorylation

Atomically precise gold nanoclusters (AuNCs) are an emerging class of quantum-sized nanomaterials with well-defined molecular structures and unique biophysical properties, rendering them highly attractive for biological applications. We set out to study the impact of different ligand shells of atomically similar nanoclusters on cellular recognition and response. To understand the effects of atomically precise nanoclusters with identical composition on cells, we selected two different water-soluble gold nanoclusters protected with captopril (Capt) and glutathione (GSH): Au₂₅(Capt)₁₈ (CNC) and Au₂₅(GSH)₁₈ (GNC), respectively. We demonstrated that a change of the ligand of the cluster completely changes its biological functions. Whereas both nanoclusters are capable of internalization, only CNC exhibits remarkable cytotoxicity, more specifically on cancer cells. CNC shows enhanced cytotoxicity by inhibiting the OXPHOS of mitochondria, possibly by inhibiting the ATP synthase complex of the electron transport chain (ETC), and by initiating the leakage of electrons into the mitochondrial lumen. The resulting increase in both mitochondrial and total cellular ROS triggers cell death indicated by the appearance of cellular markers of apoptosis. Remarkably, this effect of nanoclusters is independent of any external light source excitation. Our findings point to the prevailing importance of the ligand shell for applications of atomically precise nanoclusters in biology and medicine.

Varying protein architectures in 3-dimensions for scaffolding and modulating properties of catalytic gold nanoparticles

Fabrication and development of nanoscale materials with tunable structural and functional properties require a dynamic arrangement of nanoparticles on architectural templates. The function of nanoparticles not only depends on the property of the nanoparticles but also on their spatial orientations. Proteins with self-assembling properties which can be genetically engineered to varying architectural designs for scaffolds can be used to develop different orientations of nanoparticles in three dimensions. Here, we report the use of naturally self-assembling bacterial micro-compartment shell protein (PduA) assemblies in 2D and its single-point mutant variant (PduA[K26A]) in 3D architectures for the reduction and fabrication of gold nanoparticles. Interestingly, the different spatial organization of gold nanoparticles resulted in a smaller size in the 3D architect scaffold. Here, we observed a two-fold increase in catalytic activity and six-fold higher affinity toward TMB (3,3',5,5'-tetramethylbenzidine) substrate as a measure of higher peroxidase activity (nanozymatic) in the case of PduA[K26A] 3D scaffold. This approach demonstrates that the hierarchical organization of scaffold enables the fine-tuning of nanoparticle properties, thus paving the way toward the design of new nanoscale materials.

Chiral recognition of naproxen enantiomers based on fluorescence quenching of bovine serum albumin-stabilized gold nanoclusters

A simple, fast and green method for chiral recognition of S- and R-naproxen has been introduced. The method was based on quenching of the fluorescence intensity of bovine serum albumin-stabilized gold nanoclusters in the presence of naproxen enantiomers. The quenching intensity in the presence of S-naproxen was higher than R-naproxen when phosphate buffer solution at pH7.0 was used. The chiral recognition occurred due to steric effect between bovine serum albumin conformation and naproxen enantiomers. Two linear determination range were established as 7.4×10^-7-9.1×10^-6 and 9.1×10^-6-3.1×10^-5molL^-1 for both enantiomers and detection limits of 7.4×10^-8molL^-1 and 9.5×10^-8molL^-1 were obtained for S- and R-naproxen, respectively. The developed method showed good repeatability and reproducibility for the analysis of a synthetic sample. To make the procedure applicable to biological samples, the removal of heavy metals from the sample is suggested before any analytical attempt.

Protein-directed synthesis of Bi2S3 nanoparticles as an efficient contrast agent for visualizing the gastrointestinal tract

BSA@Bi₂S₃ nanoparticles can be applied for CT imaging of the gastrointestinal tract, realizing the visualization of gastrointestinal structures.