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A new electrochemical DNA biosensor based on double-probe mode and enzyme-mediated multiple signal electrocatalysis is constructed for the highly sensitive determination of double-stranded (ds-) PML/RARα fusion gene. Through the ingenious design of two groups of detection probes, including two thiolated capture probes anchored on dual standalone detection units integrated into one customized gold electrode and four biotinylated reporter probes, hybridizing with different segments of the same target single-stranded DNA (ssDNA) simultaneously, the hybridization efficiency between the probes and target is improved by preventing the reannealing of the two separate target ssDNA. Compared with a single reporter probe, this method can dramatically increase the amount of biotin and introduce numerous streptavidin-labelled horseradish peroxidase (HRP), thereby significantly amplifying electrochemical signals with low background signals. The combination of the dual-probe mode, multiple signal amplification strategy, and the inherent electrocatalytic activity of the HRP results in the prominent electrochemical sensing performance in detecting large-fragment target dsDNA with a detection limit as low as 71 fM. Furthermore, taking advantage of the new detection strategy, polymerase chain reaction (PCR) products and enzyme-digested PCR products from NB4 cells can be effectively analysed, showing great promise for the development of a new class of point-of-care platforms for disease-/drug-related genes.

This report outlines an ultrasensitive electrochemiluminescence (ECL) sensing platform based on water-soluble tungsten oxide quantum dots (WOx QDs) for the detection of dopamine (DA) released from P12 cells. The WOx QDs with good stability and water solubility were prepared by a facile and green hydrothermal method, and used to modify a glassy carbon electrode (WOx QDs/GCE). The proposed ECL sensor exhibited a stable and strong cathodic ECL signal when potassium peroxodisulfate (K2S2O8) as the coreactant in aqueous solution. The possible ECL mechanism was studied and deduced, and the ECL response signal of the proposed sensor decreased rapidly in the presence of dopamine (DA). Under optimal conditions, the ECL signals of WOx QDs linearly decreased with the increase of DA concentration in the range of 10−15 M to 10−9 M and 10−9 M to 10−5 M, respectively. The detection limit was as low as 10−15 M (S/N = 3). Based on these results, this method has been successfully applied to the determination of DA released by PC12 cells. The detection linear range for the detection of DA released by PC12 cells was from 0.1 to 0.9 μM with a detection limit of 0.045 μM. Therefore, the proposed ECL sensor displayed high sensitivity, good specificity and long-term stability, which may shed light on a new way to construct other high-performance ECL detection systems based on WOx or WOx QDs-based nanocomposites.

Three-dimensional (3D) cell culture system, as an alternative approach for traditional cell culture, attracts great attention because of physiological relevance and great microenvironment similarity to human conditions. Herein, a facile paper-polylactic (PLA) platform that was fabricated by wax printing and 3D printing, coupled with electrochemical sensor, was designed for the construction and intervention of 3D cell damage model. Pheochromocytoma cells (PC12) and bone marrow mesenchymal stem cells (BMSCs) were seeded on the paper-PLA 3D platforms and displayed the features of uniform distribution, good adhesion and perfect proliferation, as well as decreased circularity when compared to those grown on the two-dimensional (2D) interfaces. The electrochemical sensors revealed cell viability by monitoring dopamine released by cell models, ascertaining the applicability of the paper-PLA platform to a long-term 3D cell culture and drug assessment. Additionally, the results revealed that donepezil and BMSCs-secreted active molecules exhibited stronger cytoprotective effect against amyloid-beta oligomers-induced cell damage on the paper-PLA 3D printed platforms, indicating the cell damage model and the cell intervention model were achieved successfully in the simulated in vivo physiological microenvironment. Thus, the proposed paper-PLA platform may serve as a promising candidate for efficient drug screening and toxicity evaluation due to its simple structure, low cost, and convenient integration of 3D cell culture and activity evaluation.

This report outlines a rapid and highly sensitive colorimetric sensing platform based on a novel water-soluble WOx quantum dots (QDs) as enzymatic mimics. The WOx QDs, synthesized by a green hydrothermal method, were proven to possess excellent intrinsic peroxidase-like activity. The peroxidase substrate, 2, 2′-azinobis (3-ethylbenzthiazoline-6-sulfonic acid) diammonium salt (ABTS) could be catalyzed oxidation by WOx QDs quickly in the present of H2O2 to form a green color. Due to its excellent properties such as excellent water-solublity, good biocompatibility, easy preparation, and high stability, the proposed system showed typical Michaelis-Menten kinetics and high affinity for ABTS and H2O2, indicating WOx QDs can be used as satisfactory peroxidase mimics. Together with the fast detection process, WOx QDs-based colorimetric sensing system provided a facile, sensitive, and accurate method for the determination of H2O2 and glucose. The real glucose samples in human serum samples were detected with satisfying results. The proposed sensing platform not only expands the applications of WOx and WOx QDs-based nanocomposites, but also provides an alternative technique for biological, biomedical and environmental sample assay.

In this work, bimetallic Bi/Pt nanoparticles in bovine serum albumin biomolecular scaffold (BSA-Bi/PtNPs) were synthesized through a facile and green method. As compared with BSA-PtNPs, the BSA-Bi/PtNPs possess enhanced peroxidase-like catalytic activity. Moreover, the BSA-Bi/PtNPs are stable in harsh conditions such as high temperature, extreme pH environments, and high ionic strength, as well as in common biological matrixes. These prominent advantages enable the BSA-Bi/PtNPs to be applied to a wide range of fields. Bioassays, such as serum glucose detection, extracellular hydrogen peroxide (H 2 O 2 ) monitor, and cancer cells labeling, have been realized with satisfying results. The linear range of glucose determination was from 1 to 100 μM and the limit of detection (LOD) was 0.2 μM. The H 2 O 2 released from each MCF-7 cell after stimulation was calculated to be 2.66 × 10 −16 mol/s. By utilizing folic acid as a recognition element, tumor cell could be readily distinguished by BSA-Bi/PtNPs and the LOD for MCF-7 cell detection was 90 cells.

Sepsis has always been a severe clinical problem in critical care medicine due to its rather high mortality and poor prognosis. The current study reported for the first time a practical immunosensor for fibronectin (FN) detection in human serum by electrochemistry. A simple but robust sandwich-type strategy was employed without any complex design or material modifications, which exhibited a linear calibration plot over the 15.625–500 ng/mL concentration range and a detection limit of 15 ng/mL. The results showed that the proposed strategy displayed an excellent selectivity against other non-target substances in human serum, a higher accuracy and a better stability when compared with the traditional enzyme-linked immunosorbent assay (ELISA) in detecting the same or mixed serum from 21 healthy subjects. Furthermore, the proposed electrochemical immunosensor successfully monitored the level of serum FN at various time points in five septic patients during the treatment. These findings demonstrate that the proposed strategy is highly sensitive and accurate in monitoring sepsis progress and has significant clinical improvements over the ELISA methodology, signifying a great potential of a commercial kit.

Colorimetric recognition and sensing of sulfide with high sensitivity was proposed based on target-induced shielding against the peroxidase-like activity of bare gold nanoparticles. Significant features of the new assay system are its simplicity and cost-effectiveness. The recognition of sulfide by bare gold nanoparticles can be fulfilled in a few seconds and the assay can be accomplished in about 10 min. Furthermore, the new assay system does not require surface modification of GNPs to obtain the specificity for sulfide, and a salt-induced aggregation step is not needed. The detection limit of this method for sulfide was 80 nM. These features make this sensor a potentially powerful tool for the quantitative determination of sulfide in water samples.

An ultrasensitive electrochemical impedance spectroscopic deoxyribonucleic acid biosensor has been developed based on the conformational change of the deoxyribonucleic acid recognition interface with lodging probes. Pairing process leads to desorption of deoxyribonucleic acid bases from the gold surface, leading to a significant change of the interfacial conformation and the charge transfer resistance. Remarkably low detection limits down to 40 fM are thus obtained without any additional amplification step.

Herein, we reported for the first time that gold nanoparticles-catalyzed 3,3',5,5'-tetramethylbenzidine-H2O2 system can serve as an ultrasensitive colorimetric pH indicator. Gold nanoparticles acted as a catalyst and imitated the function of horseradish peroxidase. The absorbance at 450 nm of the yellow-color product in the catalytic reaction exhibited a linear fashion over the pH range of 6.40-6.60. On the basis of this property, we constructed a novel sensing platform for the determination of urea, urease, and urease inhibitor. The limit of detection for urea and urease was 5 μM and 1.8 U/L, respectively. The half-maximal inhibition value IC50 of acetohydroxamic acid was found to be 0.05 mM. Urea in human urine and urease in soil were detected with satisfied results.

A novel electrochemical DNA biosensor based on graphene-three dimensional nanostructure gold nanocomposite modified glassy carbon electrode (G-3D Au/GCE) was fabricated for detection of survivin gene which was correlated with osteosarcoma. The G-3D Au film was prepared with one-step electrochemical coreduction with graphite oxide and HAuCl4 at cathodic potentials. The active surface area of G-3D Au/GCE was 2.629cm(2), which was about 3.8 times compared to that of a Au-coated GCE under the same experimental conditions, and 8.8 times compared to a planar gold electrode with a similar geometric area. The resultant nanocomposites with high conductivity, electrocatalysis and biocompatibility were characterized by scanning electron microscopy (SEM), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). A "sandwich-type" detection strategy was employed in this electrochemical DNA biosensor and the response of this DNA biosensor was measured by CV and amperometric current-time curve detection. Under optimum conditions, there was a good linear relationship between the current signal and the logarithmic function of complementary DNA concentration in a range of 50-5000fM with a detection limit of 3.4fM. This new biosensor exhibited a fast amperometric response, high sensitivity and selectivity and has been used in a polymerase chain reaction assay of real-life sample with a satisfactory result.