Modulating Polarization of Perovskite-Based Heterostructures via In Situ Semiconductor Generation and Enzyme Catalysis for Signal-Switchable Photoelectrochemical Biosensing.

Polarization of photoactive materials in current photoelectric (PE) systems is difficult to be adjusted, and thus electron-transfer routes of these systems are unchangeable, which limits their performance in photoelectrochemical (PEC) analysis. Herein, we attempted to modulate the polarization of perovskite-based heterostructures by both in situ semiconductor generation and enzyme catalysis. Owing to their band alignments, Cs3Bi2Br9 quantum dots (QDs) and BiOBr are confirmed to construct a Z-scheme structure, leading to a large anodic photocurrent. In the presence of ascorbic acid 2-phosphate (AAP), BiPO4 is generated on the surface of the Cs3Bi2Br9 QDs/BiOBr heterostructure, reassigning energy bands of BiOBr. Accordingly, polarization of the photoactive materials is converted, and a new Z-scheme structure with a reversed electron-transfer route is constructed, which leads to an evident cathodic photocurrent. Furthermore, abundant electron donors can be obtained by catalyzing AAP with alkaline phosphatase (ALP). In this case, photogenerated holes in BiOBr are preferentially annihilated by electron donors, thereby blocking transfer of photogenerated electrons in the Cs3Bi2Br9 QDs/BiOBr/BiPO4 heterostructure. Consequently, a second polarization conversion is triggered by enzyme catalysis, resulting in the recovery of an anodic photocurrent. Benefited from the polarization conversion, a PEC biosensor with a feature of two-wing signal switch is designed, which remarkably enlarges the range of the signal response and subsequently improves the analytical performance. As a result, ALP in small volume of human serum can be quantified with this method. In this work, polarization of perovskite-based photoactive materials is tuned, proposing an alternative perspective on the design of advanced PE systems.

Applications of DNA-nanozyme-based sensors.

Since the discovery of the enzyme-like activities of nanomaterials, the study of nanozymes has become one of the most popular research frontiers of diverse areas including biosensors. DNA also plays a very important role in the construction of biosensors. Thus, the idea of combined applications of nanozymes with DNA (DNA-nanozyme) is very attractive for the development of nanozyme-based biosensors, which has attracted considerable interest of researchers. To date, many sensors based on DNA-functionalized or templated nanozymes have been reported for the detection of various targets and highly accelerated the development of nanozyme-based sensors. In this review, we summarize the main applications and advances of DNA-nanozyme-based sensors. Additionally, perspectives and challenges are also discussed at the end of the review.

Nucleic acid-based ratiometric electrochemiluminescent, electrochemical and photoelectrochemical biosensors: a review.

The demand of precise assay of nucleic acids and other bioanalytes has been increasing enormously in various areas including point-of-care diagnostics, military, environmental monitoring and so on. Compared with other nucleic acid biosensors, the electrochemical nucleic acid biosensors possess a range of merits like amenable miniaturization, low costs and high sensitivity. Ratiometric electrochemical nucleic acid biosensors can overcome the inherent systematic errors of conventional electrochemical biosensors and enhance the reproducibility and credibility. This short review (with 81 refs.) summarizes the evolvements made in the area of nucleic acid-based biosensors based on ratiometric (electrochemiluminescent, electrochemical and photoelectrochemical) readout in the past few years. Many of the methods discussed here are based on the use of advanced nanomaterials such as quantum dots, graphitic carbon nitrides, graphene oxide, C-dots, gold nanoparticles, metal-organic frameworks, and respective nanohybrids. Three sections (on electrochemiluminescence, classical electrochemical and emerging photoelectrochemical systems) demonstrate the merits of ratiometric assays in various applications. The review ends with a section with conclusions and a discussion of future perspectives. Graphical abstract Ratiometric sensing strategies overcome the intrinsic systematic errors of conventional electrochemical sensors that suffer from environmental and personal factors, and thus leads to remarkably enhanced reproducibility and reliability.

A versatile switchable dual-modal colorimetric and photoelectrochemical biosensing strategy via light-controlled sway of a signal-output transverter.

A design criterion to construct a versatile dual-modal colorimetric and PEC biosensing platform for switching the corresponding mode freely is proposed via integration of a natural enzyme, light-activated nanozyme and light-controlled swayable signal-output transverter. A switchable dual-modal platform toward DNA analysis is developed as a proof of concept.

An enzyme cascade sensor with resistance to the inherent intermediate product by logic-controlled peroxidase mimic catalysis.

Enzyme cascade sensors usually could not discriminate between the target and intermediate product. Herein, based on "AND" logic-controlled activation of the glucose oxidase-copper peroxide sensing system, enzyme cascade detection for glucose with resistance to inherently existing intermediate product H2O2 was reported for the first time, which may provide a novel way for facilitating enzyme cascade sensing.

Simulated enzyme inhibition-based strategy for ultrasensitive colorimetric biothiol detection based on nanoperoxidases.

In this work, a simulated enzyme inhibition-based strategy was transplanted from natural peroxidase-based sensing methods for colorimetric nanoperoxidase-based biothiol detection. This work might provide some new perspectives for the construction and biomimetic regulation of mimicked biological signalling systems based on nanoperoxidases.

Direct Electrochemical Vibrio DNA Sensing Adopting Highly Stable Graphene-Flavin Mononucleotide Aqueous Dispersion Modified Interface.

A biofunctionalized graphene nanohybrid was prepared by simultaneously sonicating graphene and riboflavin 5'-monophosphate sodium salt (FMNS). FMNS, as a biodispersant, showed an efficient stabilization for obtaining highly dispersed graphene nanosheets in an aqueous solution. Due to the superior dispersion of graphene and the excellent electrochemical redox activity of FMNS, a direct electrochemical DNA sensor was fabricated by adopting the inherent electrochemical redox activity of graphene-FMNS (Gr-FMNS). The comparison between using traditional electrochemical indicator ([Fe(CN)6]3-/4-) and using the self-signal of Gr-FMNS was fully conducted to study the DNA-sensing performance. The results indicate that the proposed DNA-sensing platform displays fine selectivity, high sensitivity, good stability, and reproducibility using either [Fe(CN)6]3-/4- probe or the self-signal of Gr-FMNS. The two methods display the same level of detection limit: 7.4 × 10-17 M (using [Fe(CN)6]3-/4-) and 8.3 × 10-17 M (using self-signal), respectively, and the latter exhibits higher sensitivity. Furthermore, the sensing platform also can be applied for the DNA determination in real samples.