A sensitive and simple competitive nanozyme-linked apta-sorbent assay for the dual-mode detection of ochratoxin A.

The enzyme-linked apta-sorbent assay (ELASA) is widely used for the detection of small-molecule compounds as a result of low cost and reagent stability of aptamers. However, enzyme labels used in ELASA still suffer from some drawbacks, such as high production cost and limited stability. To overcome the drawbacks, we reported a nanozyme-linked apta-sorbent assay (NLASA) coupled with surface-enhanced Raman scattering (SERS)-colorimetric dual-mode detection. For nanozyme labels, Pd-Pt bimetallic nanocrystals (Pd-Pt NRs) could catalyze 3,3',5,5'-tetramethylbenzidine (TMB) to blue TMB2+, whose color variation could not only be distinguished by naked eyes but also had a strong SERS signal. The NLASA method was employed to detect ochratoxin A (OTA) with a limit of detection values of 0.097 nM (0.039 ppb) and 0.042 nM (0.017 ppb) via the colorimetric and SERS methods, respectively. This method was applied for the determination of OTA in wine and grape samples, and the detection results were in a satisfied agreement with those determined by the high performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS) method. The proposed NLASA method provided a rapid and sensitive detection for OTA and could also be broadened for other small-molecules.

Lysozyme regulates the extracellular polymer of activated sludge and promotes the formation of electroactive biofilm.

The formation of electroactive biofilm from activated sludge on electrode surface is a key step to construct a bio-electrochemical system, yet it is greatly limited by the poor affinity between the bacteria and the electrode interface. Herein, we report a new method to promote the formation of electroactive biofilm by regulating the extracellular polymeric substance (EPS) content in activated sludge with lysozyme. The investigation of the effect of lysozyme treatment on the content of extracellular polymers and the biofilm formation of electroactive bacteria suggests that lysozyme can improve the permeability of the positive bacterial cell membrane and thus increase the EPS content in the activated sludge. The characterizations of electrochemical activity, surface morphology and community structure of the anode biofilm indicate that increasing EPS content promotes the adhesion of the mixed bacteria in the activated sludge on the electrode and results in denser biofilms with better conductivities. The microbial fuel cell (MFC) inoculated with the sludge of high EPS content exhibits the power density up to 2.195 W/m2, much higher than that inoculated with the untreated sludge (1.545 W/m2). The strategy of adjusting EPS content in activated sludge with a biological enzyme can effectively enhance the ability of the bacterial community to form biofilms and exhibits great application potentials in the construction of high efficiency bio-electrochemical systems.

Mercury speciation based on mercury-stimulated peroxidase mimetic activity of gold nanoparticles.

Mercury speciation is of significant importance in environmental and biological analysis because its toxicity and metabolic behavior in the human body differ among species. Nanomaterial-assisted optical sensors are widely used for mercury ion detection but rarely applied in mercury speciation analysis. In this work, we develop a novel colorimetric sensing strategy for mercury speciation based on mercury-stimulated peroxidase mimetic activity of gold nanoparticles with the assistance of different reductants. In the presence of a weak reductant, only inorganic mercury can be reduced to Hg0, whereas both inorganic mercury and organic mercury can be reduced to Hg0 in the presence of a strong reductant. Due to the high affinity between Hg and Au, Hg0 deposits on the AuNP surface in the form of a Au-Hg amalgam, leading to a remarkable enhancement of peroxidase mimetic activity of gold nanoparticles. On the basis of this effect, inorganic mercury and total mercury can be detected by using 3,3',5,5'-tetramethylbenzidine (TMB) as the substrate. The limits of detection for inorganic mercury and total mercury are 1.9 and 0.9 nM within 5-100 nM, respectively. The selectivity of this sensing system is high due to the specificity of Au-Hg interaction. Its practical applications are further demonstrated by organic mercury analysis in a fish sample and mercury speciation in a human hair sample.

Improving the power generation performances of Gram-positive electricigens by regulating the peptidoglycan layer with lysozyme.

The power generation performance of a microbial fuel cell (MFC) greatly depends on the relative amount of electricigens in the anodic microbial community. Running the MFC multiple times can practically enrich the electricigens, and thus improve its power generation efficiency. However, Gram-positive electricigens cannot be enriched well because of their thick non-conductive peptidoglycan layer. Herein, we report a new Gram-positive electricigen enrichment method by regulating the peptidoglycan layer of the bacteria using lysozyme. Lysozyme can partially hydrolyze the peptidoglycans layer of Gram-positive Firmicutes to improve the permeability of cell wall, and thus enhance its electricity generation activity. The stimulation of Gram-positive electricigen endows MFCs a high power generation community structure, which results in the power density 42% higher than that of the control sample. Our work has provided a new and simple method for optimizing the anode community structure by regulating weak electricigens in the community with lysozyme.

Discrimination of antibiotic-resistant Gram-negative bacteria with a novel 3D nano sensing array.

A novel sensor array based on a (+)AuNP/AuNC nanocomposite was constructed for the selective discrimination of 10 types of Gram-negative bacteria (including 3 types of antibiotic-resistant strains) at a low concentration level of OD600 = 0.015. By recognizing the triple optical patterns of Gram-negative bacteria with the assistance of LDA, the sensor array is able to group the bacteria with respect to their species to each other.