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Abstract A simple, rapid, and sensitive homogeneous electrochemical bleomycin (BLM) bioassay has been successfully developed through the target-induced specific/efficient cleavage reaction. The designed probe, denoted as MB-DNA, contains both methylene blue (MB) and target recognizable sequences, and presents relatively low electrochemical signal. Upon the addition of BLM, the recognition/cleavage reaction occurs and leads to the in-situ generation of MB tag (MB-DNA-1), leading to the reduced electrostatic repulsive force. As a result, an obvious enhancement in differential pulse voltammetry (DPV) current is determined, which is relied on the amount of BLM. Thus, a turn on homogeneous electrochemical method for BLM is really achieved, and exhibits high sensitivity of 33 pM, and the shortest response time of 20 min. Furthermore, this electrochemical bioassay presents excellent sensing performance in the analysis of BLM in real samples. Comparing with other sensing strategies for BLM, this proposed electrochemical platform is just consisted of one DNA probe alone, and affords a really rapid and sensitive strategy for BLM analysis. Graphical abstract A novel diffusivity-mediated turn-on homogeneous electrochemical biosensor with the advantageous of simplicity, rapidness, and sensitivity was successfully developed for BLM determination based on target-induced specific cleavage reaction fx1 Highlights • A homogeneous electrochemical strategy for BLM detection was developed. • It's based on the target-induced diffusivity enhancement of MB toward ITO electrode. • It has the features of simplicity, rapidness, and sensitivity. • It has been successfully applied for the analysis of BLM in human serum samples. [ABSTRACT FROM AUTHOR]

We proposed, for the first time, a ultrasensitive amplification-free, label-free, and enzyme-free homogeneous electrochemical cytosensing platform based on the target-induced displacement reaction for tumor cell “signal-on” assay. To realize this proposal, the electroactive probe, [Fe(CN) 6 ] 3− , was entrapped in the pores of positively charged MSN (PMSN), and then the negatively charged aptamer of the tumor cell was adsorbed on the surface of PMSN as a biogate. Once the tumor cells were recognized and captured by the aptamer, the biogate could be efficiently opened and the entrapped [Fe(CN) 6 ] 3− released, which can be ascribed to the decreased adhesion between the aptamer-cell complex and PMSN. Consequently, the electrochemical signal dramatically increased. Overall, the “signal-on” strategy was conveniently realized. Notably, the detection limit for tumor cells assay (13 cells/mL) is comparable to those of the reported methods Furthermore, based on the similar proposal, this biosensor also can be extended for the ultrasensitive detection of microRNA (38 aM, S/N = 3) and Hg 2+ (0.47 pM, S/N = 3). Therefore, this biosensing platform has the great potential to be a powerful tool in the applications of disease diagnostics and environmental monitoring. [ABSTRACT FROM AUTHOR]

• A nonlinear frequency–amplitude model for viscoelastic devices is proposed. • A generalized complex stiffness model is proposed to characterize frequency dependence. • A dynamic analysis method for viscoelastic structures is established. • Property tests are conducted to verify the proposed mechanical models. Owing to the complex mechanical properties influenced by excitation frequency and amplitude, the modeling of viscoelastic damping materials and devices faces the challenge of poor coordination among simplicity, accuracy, generality and flexibility. To address this issue, a nonlinear frequency–amplitude model was established by combining the proposed generalized complex stiffness model with the Berg friction model. The generalized complex stiffness model was proposed to characterize the frequency dependence, and the Berg friction model was employed to study the amplitude dependence. A dynamic analysis method was proposed based on a state space approach to realize a complete and accurate representation of the proposed mechanical model. Property tests of a viscoelastic damper and viscoelastic isolator were then conducted to study the dynamic mechanical performance under different excitation frequencies and amplitudes. Finally, the accuracy of the nonlinear frequency–amplitude model was validated using experimental data. [ABSTRACT FROM AUTHOR]

A novel “ON–OFF” switchable enzymatic biofuel cell (EBFC), controlled by in situ thermal-stimuli signal, has been consciously designed. Poly ( N -isopropylacrylamide) (PNIPAm) chains were used to act as “ON” and “OFF” channels. Consecutively switching of temperature below and above the lower critical solution temperature (LCST), the reversible conformation changing of the PNIPAm chains between superhydrophilicity and superhydrophobicity was achieved, which constructed the “ON” and “OFF” channel for the transfer of the electrochemical probe to the underlying electrode correspondingly. Gold nanoparticles (AuNPs) protected glucose oxidase and laccase were successfully entrapped into the intelligent thermal-sensitive PNIPAm chains, and performed as the catalysts for the oxidation of glucose and the reduction of O 2 , respectively. Below the LCST, the fuels and the mediator could access to the catalytic centers of enzymes (set as “ON” state); while above the LCST, the reaction was impeded because the process of reactant transmission was blocked (set as “OFF” state). By switching the “valve” of mass transfer, the fabricated EBFC displayed the obvious “ON–OFF” controllable behavior. At the “ON” state, the open circuit voltage ( E cell ocv ) and maximal power output density ( P max ) could reach to 0.70 V and 20.52 μW cm −2 , respectively; while at the “OFF” state, the E cell ocv and P max were only 0.30 V and 3.28 μW cm −2 correspondingly. The switchable process was repeatable, and the response time was only several minutes. [ABSTRACT FROM AUTHOR]

Biofuel cells (BFCs) can directly produce electrical energy from biofuels, have been applied as the power source to construct self-powered biosensors (SPBs) for analyte sensitive detection through changing their outputs with the concentration of analyte. Compared with conventional electrochemical sensors, BFCs-based SPBs no longer required the external power supplies and other complex devices, which are conducive to the development of portable and implantable devices. The output performance and stability of BFCs are the key issues for constructing SPBs with excellent performance. Based on the above-mentioned issues, researchers continue to develop new strategies and novel nanomaterials for sensor design, and build BFCs-based SPBs with good stability and high output performance by improving the stability and catalytic activity of catalysts. So far, BFCs-based SPBs have achieved gratifying progresses through the continuous exploration of researchers. In this review, we summarize the research advances in SPBs based on different nanocatalytic systems, such as enzymes/nanomaterials-based, light-driven, and non-enzymes-based, and discuss the novel SPBs based on different sensing strategies. Apart from this, we also summarize and discuss the improvement of the stability and durability of SPBs by the nanocatalytic system. Finally, we propose the challenges and opportunities of BFCs-based SPBs in the future development directions. [Display omitted] The research advances in self-powered biosensors based on different nanocatalytic systems were reviewed, including enzymes/nanomaterials-based, light-driven and non-enzymes-based strategy. • The research advances in SPBs based on different nanocatalytic systems were reviewed. • Enzymes/nanomaterials-based, light-driven and non-enzymes-based SPBs were summarized. • The challenges and opportunities of SPBs in the future development were discussed. [ABSTRACT FROM AUTHOR]

Graphical abstract A nonfluorescent AIE-Au nanoconjugate was successfully prepared through the electrostatic interaction based on aggregation induced emission nanoparticle and gold nanoparticle, and was further applied in highly sensitive analysis of acetylcholinesterase activity and inhibitor. Highlights • AIE-Au nanoconjugate with ultralow background noise was successfully fabricated. • It was applied as fluorescence nanosensor for AChE and inhibitor assay. • It presented sufficient sensitivity for carbaryl biosensing in real sample. Abstract Fluorescence nanosensor with ultralow fluorescence background is in highly demand for enhancing the sensing performance. Herein, we report a kind of nonfluorescent nanoconjugates between aggregation induced emission nanoparticles and gold nanoparticles (denoted as AIE-Au nanoconjugates) through electrostatic interaction, and further implement them in sensitive analysis of acetylcholinesterase (AChE) activity and inhibitors. Acetylthiocholine (ATCh) was effectively catalyzed by AChE and subsequently hydrolysized into thiocholine, which interacted with AuNPs via the relatively strong Au-S bonds leading to the separation of AIE nanoparticles and AuNPs to recover AIE nanoparticles' fluorescence. Further, the proposed biosensor provided an ultrahigh sensitivity of 0.015 mU/mL for AChE. In view of the fact that AChE activity can be prohibited by inhibitors, AIE-Au nanoconjugates can also be applied for carbaryl analysis. On account of the exceptional properties, the prepared AIE-Au nanoconjugates broaden the perspectives of AIE nanoparticles and AuNPs for biosensor development, and demonstrated significant application prospect in food safety. [ABSTRACT FROM AUTHOR]

In this work, we develop a facile one-step synthesis method of poly(3,4-dihydroxyphenylalanine) (poly(DOPA)) fluorescent organic nanoparticles (FONPs) by polymerization of DOPA in alkaline alcohol solution under ultrasonic radiation. The morphology and size of poly(DOPA)-FONPs are dependent on the synthesis conditions, such as solvent and alkali concentration. Under the optimized condition, the prepared poly(DOPA)-FONPs possess not only uniform size and morphology, but also strong green fluorescence, good solubility in water and organic solvents. Under excitation of single wavelength, two emission peaks can be clearly observed, which are pH-sensitive. Moreover, the intensity ratio of two emission peaks is linear against pH values from 4.0 to 8.0 in buffer solution. In addition, the pH-sensitive response of the poly(DOPA)-FONPs be free from the influence of various metal ions and biomolecules, indicating the excellent specificity to pH. Further, due to the excellent biocompatibility, the poly(DOPA)-FONPs might also be applied on biological imaging for monitoring intracellular pH. The as-prepared poly(DOPA)-FONPs would be promising to be applied on the low-cost, low-toxic and label-free ratiometric pH sensor. [ABSTRACT FROM AUTHOR]

Abstract: An electrochemiluminescence (ECL) inhibition method combined with molecularly imprinted solid phase extraction (MISPE) was developed for quantitative determination of phenolphthalein in drug, slimming food and human plasma. Phenolphthalein could strongly inhibit the ECL signal of /2-(dibutylamino)ethanol (DBAE) system that was used as the basis of the analysis. Molecularly imprinted polymers (MIPs) were synthesized as solid phase extraction (SPE) sorbents, and MISPE protocol was developed for the selective extraction and purification of phenolphthalein. Under the optimized conditions, quenched ECL intensity versus the logarithm of the concentration of phenolphthalein was in good linear relationship over a concentration range from 3.18×10−10 to 1.59×10−7 g/mL and the detection limit was 1.0×10−10 g/mL. High affinity and selectivity of MISPE enabled the successful application of this method to determine phenolphthalein in drug, slimming food and human plasma. Further, a possible mechanism for the quenching effects of /DBAE system by phenolphthalein was also proposed. [Copyright &y& Elsevier]

Abstract: A gas chromatography-mass spectrometry assay was developed and successfully applied for the determination of phthalates in ham sausage migrated from packaging film. The phthalates studied were dimethyl phthalate (DMP), diethyl phthalate (DEP), dibutyl phthalate (DBP), benzylbutyl phthalate (BBP), bis(2-ethylhexyl) phthalate (DEHP) and di-n-octyl phthalate (DNOP) , with dibutyl adipate (DBA) as internal standard. The sample pre-treatments included extraction with n-hexane, solvent evaporation and reconstitution with acetonitrile before and after solid-phase extraction (SPE). The extraction and cleaning up procedure was carried out with cartridges containing dimethyl butylamine groups, which showed extraction efficiencies over 87.3%. The calibration curves obtained were linear with correlation coefficients greater than 0.99. The method proved to be accurate and precise for the six phthalates used. It was successfully applied to a study on the migration of phthalates from packaging PVC film into ham sausage. [Copyright &y& Elsevier]

Biofuel cells (BFCs)-based self-powered biosensors suffer from the limited stability of bioenzymes. Meanwhile, the poor performance of self-powered biosensors affects the sensitivity of biosensing, thus, it is significant and challenging to improve their stability and sensitivity. In our work, a BFC-based self-powered biosensor, with simultaneously enhanced stability and sensitivity, was constructed utilizing dual metal-organic frameworks (MOFs) as the carriers of the bioenzyme and the electroactive probe, respectively. Anodic enzyme, glucose dehydrogenase (GDH), was encapsulated in zeolitic imidazolate framework-8 (ZIF-8) to form GDH@ZIF-8 composites, enhancing the catalytic activity and stability of GDH. Meanwhile, another zirconium metal-organic frameworks (UiO-66-NH 2) loaded with electroactive molecules (K 3 [Fe(CN) 6 ]) served as nano-enrichment carriers and improved the capability of the cathode to accept electrons from the anode, further improving the sensitivity of the as-proposed biosensor. Herein, the "signal-on" BFC-based self-powered biosensing of exosomes, the model analyte, with excellent stability and outstanding sensitivity was realized with the assistance of dual MOFs, and the detection limit was down to 300 particles mL−1 (based on 3s/k), which was superior to those previously reported in literatures. Furthermore, the developed protocol was capable of detecting exosomes derived from cancer cells in complex biological samples. Overall, in this work the enhancement of both stability and sensitivity has been achieved by utilizing two types of MOFs, which laid the foundation for expanding the applications of BFC-based self-powered biosensors. • GDH@ZIF-8 composites can enhance the catalytic activity and stability of GDH. • Nano-enrichment carriers entities ([Fe(CN) 6 ]3-/UiO-66) was designed. • The as-proposed biosensor with excellent stability and high sensitivity was realized for exosomes detection. • The detection limit was down to 300 particles mL−1, which was much lower than those previously reported results. [ABSTRACT FROM AUTHOR]

Early and accurate disease diagnosis is of great appeal for saving patients' life, but requires biomarkers to be sensitively detected with simplicity, convenience, and low cost. Exploring the development of a high-performance fluorescence biosensor for biomarkers solid, equipment-free and visual biosensing is highly urgent but faces enormous challenges. Herein, we proposed a brand-new fluorescence system by integrating a typical aggregation induced emission dye (TPE-BTD) with dopamine for multiple biomarkers sensitive detection based on target-induced catalyzing oxidation. The system comprising TPE-BTD and dopamine emits strong fluorescence; with horseradish peroxidase (HRP) or HRP-mimicking DNAzyme and H 2 O 2 being added, significant oxidation on dopamine occurs to generate dopachrome, which actuated the inner filter effect (IFE) due to the overlap of its absorbtion curve and emission spectrum of TPE-BTD, subsequently decreasing fluorescence emission and displaying a rapid and sensitive response to H 2 O 2 and G-quadruplex DNA. We further apply TPE-BTD/dopamine system in analysis of glucose and DNA adenine methylation methyltransferase (Dam MTase) based on target-initiated signal transduction. Finally, TPE-BTD was employed as emitters in fabrication of paper biosensors, which can achieve solid, equipment-free and visual detection of multiple biomarkers based on the high emission performance of TPE-BTD, opening up a new pathway to development of biosensors for practical application. We expect this sensing conception will be helpful in development of practical biosensors, and this sensor will find more applications in disease diagnosis. • AIEgen and dopamine were employed to develop label-free biosensors based on IFE. • It realized H 2 O 2 , G-quadruplex DNA, glucose, and Dam MTase sensitive detection. • It was applicable for paper biosensor for equipment-free and naked-eye sensing. [ABSTRACT FROM AUTHOR]