A novel high-stability bioelectrochemical sensor based on sol-gel immobilization of lactate dehydrogenase and AuNPs-rGO signal enhancement for serum pyruvate detection

An "off-on" fluorescent probe for imaging pyruvic acid in living systems

Pyruvic acid (PA) is an α-keto acid which exert important biological and pathological functions. The current PA profiling assays are mainly based on the ultraviolet spectroscopy and electrochemical biosensor, requiring killing cells and destroying tissues which limit their application in living cells. Optical imaging provides nondestructive powerful and detective tools to better understand the physiological and pathological role of PA in living systems. However, as far as we know, none of"off - on" PA fluorescent sensor has been developed. Herein, we reported a PA recognition reaction that arylhydroxylamine group could be selectively reduced to acetylamide group by PA. With this recognition reaction, a fluorescence probe (FPA) based on the photoinduced electron transfer (PET) pathway was designed, synthesized and could release strong fluorescence at 447 nm. We proved that FPA could detect PA in aqueous solution, living cells, Caenorhabditis elegans and the roots of Arabidopsis thaliana with good selectivity and sensitivity as low as 0.42 μM. In addition, we successfully using probe FPA to study the intracellular PA production pathway in cells and evaluated its physiological level in Arabidopsis roots at different growth stages. The results show that the physiological level of PA in Arabidopsis thaliana roots is closely associated with their growth stages, which indicated that PA might act as a carbon source and related growth signaling molecule to promote plant growth and root elongation. Therefore, we expect probe FPA to be a powerful tool to better understand the physiological and pathological role of PA.

A sensitive bromate sensor based on a gold nanoparticle-poly(diallyldimethylammonium chloride)-reduced graphene oxide nanocomposite modified glassy carbon electrode

A nanocomposite consisting of gold nanoparticles (AuNPs), poly(diallyldimethylammonium chloride) (PDDA), and reduced graphene oxide (rGO) was fabricated by a two-step chemical reduction method. Firstly, a PDDA-rGO composite was prepared by using hydrazine hydrate as a reducing agent. Subsequently, the AuNP-PDDA-rGO composite was prepared in ethylene glycol with PDDA-rGO and HAuCl4 as raw materials using sodium citrate as a reduction agent. The resulting composite was characterized using X-ray powder diffraction (XRD), Raman spectroscopy, transmission electron microscopy (TEM), and electrochemical methods. This composite was then modified on a glassy carbon electrode (GCE) by the dropping method. The electrochemical behavior of bromate on this modified electrode was investigated. The results showed that PDDA-rGO can be used as a good carrier to obtain AuNPs with small particle sizes and good dispersion. The AuNPs and PDDA-rGO in composite enhanced the electrochemical activity of the electrode. Under the synergistic action of each component, the resulting electrode exhibited high activity for the electrochemical reduction of bromate. Based on this, an amperometric bromate sensor was fabricated in N2-saturated 0.10 mol/L HCl with attractive features including a wide linear range of 1.0 × 10-7-1.7 × 10-3 mol/L, a low detection limit (3sb) of 3.2 × 10-8 mol/L, and a high sensitivity of 2317 µA/mM/cm2. The sensor was successively used for the determination of bromate in drinking water.

Inosine reverses multidrug resistance in Gram-negative bacteria carrying mobilized RND-type efflux pump gene cluster tmexCD-toprJ

Antimicrobial resistance is rapidly increasing worldwide, highlighting the urgent need for pharmaceutical and nonpharmaceutical interventions to tackle different-to-treat bacterial infections. Tigecycline, a semi-synthesis glycylcycline for parenteral administration, is widely recognized as one of the few effective therapies available against pan-drug resistant Gram-negative pathogens. Regrettably, the efficacy of multiple drugs, including tigecycline, is currently being undermined due to the emergence of a recently discovered mobilized resistance-nodulation-division-type efflux pump gene cluster tmexCD1-toprJ1. Herein, by employing untargeted metabolomic approaches, we reveal that the expression of tmexCD1-toprJ1 disrupts bacterial purine metabolism, with inosine being identified as a crucial biomarker. Notably, the supplementation of inosine effectively reverses tigecycline resistance in tmexCD1-toprJ1-positive bacteria. Mechanistically, exogenous inosine enhanced bacterial proton motive force, which promotes the uptake of tigecycline. Furthermore, inosine enhances succinate biosynthesis by stimulating the tricarboxylic acid cycle. Succinate interacts with the two-component system EnvZ/OmpR and upregulates OmpK 36, thereby promoting the influx of tigecycline. These actions collectively lead to the increased intracellular accumulation of tigecycline. Overall, our study offers a distinct combinational strategy to manage infections caused by tmexCD-toprJ-positive bacteria.

IMPORTANCE

TMexCD1-TOprJ1, a mobilized resistance-nodulation-division-type efflux pump, confers phenotypic resistance to multiple classes of antibiotics. Nowadays, tmexCD-toprJ has disseminated among diverse species of clinical pathogens, exacerbating the need for novel anti-infective strategies. In this study, we report that tmexCD1-toprJ1-negative and -positive bacteria exhibit significantly different metabolic flux and characteristics, especially in purine metabolism. Intriguingly, the addition of inosine, a purine metabolite, effectively restores the antibacterial activity of tigecycline by promoting antibiotic uptake. Our findings highlight the correlation between bacterial mechanism and antibiotic resistance, and offer a distinct approach to overcome tmexCD-toprJ-mediated multidrug resistance.

Enzyme-free electrochemical sensor platforms based on transition metal nanostructures for clinical diagnostics

The detection of emergent biomarkers is of key significance in numerous clinical, biological, and biomedical fields. Specifically, the design and development of potent electrochemical lactic acid and glucose sensing platforms are especially in great demand in a variety of industries, including those involved in clinical analysis, biomedicine, biological, food, cosmetics, pharmaceuticals, leather, sports, and chemical industries. Nanostructured transition metal-derived materials have opened the door to electrochemical sensors and biosensors due to their advantages of high surface-to-volume ratio, surface reaction activity, catalytic activity, and strong adsorption capability. The primary aim of the present minireview is to highlight the advancement of enzyme-free electrochemical sensor platforms based on transition metal-derived nanostructures with high electrocatalytic activity and sensing performance towards lactic acid and glucose in practical samples. The preparation approaches, structural and composition monitoring, fabrication of sensing electrodes, catalytic activity, sensing performance in real samples, and the exploration of sensing mechanisms are majorly concentrated on in most of our recent research studies. Moreover, state-of-the-art transition metal-derived nanostructure-derived electrochemical sensor platforms, critical comparison of the analytical performance of the sensor platforms, and the future perspectives of the enzyme-free electrochemical sensor for clinical diagnostics are described.