Dense Conductive Metal-Organic Frameworks as Robust Electrocatalysts for Biosensing

A simple and reliable interenzyme distance regulation strategy based on a DNA quadrangular prism scaffold for ultrasensitive ochratoxin A detection

Developing sensitive and accurate Ochratoxin A (OTA) detection methods is essential for food safety. Herein, a simple and reliable strategy for regulating interenzyme distance based on a rigid DNA quadrangular prism as a scaffold was proposed to establish a new electrochemical biosensor for ultrasensitive detection of OTA. The interenzyme distances were precisely adjusted by changing the sequences of the hybridized portions of hairpins SH1 and SH2 to the DNA quadrangular prism, avoiding the complexity and instability of the previous DNA scaffold-based enzyme spacing adjustment strategies. The electrochemical biosensor constructed at the optimal interenzyme distance (10.4 nm) achieved sensitive detection of OTA in a dynamic concentration range from 10 fg/mL to 250 ng/mL with a detection limit of 3.1 fg/mL. In addition, the biosensor was applied to quantify OTA in real samples, exhibiting great application potential in food safety.

Covalent organic frame based high-performance nanocomposite for construction of ATP sensor

In this work, a novel covalent organic frame (TAPT-TFPB COF) with self-enhanced photoelectric activity was prepared for decorating on conductive single-walled carbon nanotubes (SWCNT) to synthetize a high-performance photoelectric nanocomposite (COF/SWCNT), in which the interfacial charge separation and photogenerated carrier migration rate was significantly improved to obtain desiring photoelectric conversion efficiency for generating an extremely high photocurrent. Accordingly, the synthetic COF/SWCNT was ingeniously applied in the fabrication of ultrasensitive photoelectrochemical (PEC) biosensor for realizing the trace ATP detection by integrating with an Exo III-assisted dual DNA recycling amplification strategy. The recycling amplification could efficiently convert trace target ATP into plentiful output DNA, which ingeniously triggered the hybridization chain reaction (HCR) to generate a long DNA strand with substantial quencher manganese porphyrin (MnPP) loading to depress the photocurrent of COF/SWCNT. The experimental data showed that proposed biosensor had a detection range from 10 fmol L-1 to 10 nmol L-1 with the detection limit as low as 2.75 fmol L-1 (S/N = 3). In addition, this proposed biosensor showed excellent analytical performance in terms of stability, specificity and reproducibility, providing a possibility to accomplish sensitive and accurate in vitro diagnosis.

Nanozyme-Enhanced Electrochemical Biosensors: Mechanisms and Applications

Nanozymes, as innovative materials, have demonstrated remarkable potential in the field of electrochemical biosensors. This article provides an overview of the mechanisms and extensive practical applications of nanozymes in electrochemical biosensors. First, the definition and characteristics of nanozymes are introduced, emphasizing their significant role in constructing efficient sensors. Subsequently, several common categories of nanozyme materials are delved into, including metal-based, carbon-based, metal-organic framework, and layered double hydroxide nanostructures, discussing their applications in electrochemical biosensors. Regarding their mechanisms, two key roles of nanozymes are particularly focused in electrochemical biosensors: selective enhancement and signal amplification, which crucially support the enhancement of sensor performance. In terms of practical applications, the widespread use of nanozyme-based electrochemical biosensors are showcased in various domains. From detecting biomolecules, pollutants, nucleic acids, proteins, to cells, providing robust means for high-sensitivity detection. Furthermore, insights into the future development of nanozyme-based electrochemical biosensors is provided, encompassing improvements and optimizations of nanozyme materials, innovative sensor design and integration, and the expansion of application fields through interdisciplinary collaboration. In conclusion, this article systematically presents the mechanisms and applications of nanozymes in electrochemical biosensors, offering valuable references and prospects for research and development in this field.

Ultrasensitive Dual-Mode Visual/Photoelectrochemical Bioassay for Antibiotic Resistance Genes through Incorporating Rolling Circle Amplicons into a Tailored Nanoassembly

As emerging contaminants in the environment, antibiotic resistance genes (ARGs) have aroused a global health crisis and posed a serious threat to ecological safety and human health. Thus, efficient and accurate onsite detection of ARGs is crucial for environmental surveillance. Here, we presented a colorimetric-photoelectrochemical (PEC) dual-mode bioassay for simultaneous detection of multiple ARGs by smartly incorporating rolling circle amplification (RCA) into a stimuli-responsive DNA nanoassembly, using the tetracycline resistance genes tetA and tetC as models. The tailored DNA nanoassembly containing RCA amplicons hybridized with specific signal probes: CuO nanoflowers-anchored signal DNA1 and HgO nanoparticles-anchored signal DNA2, respectively. Upon exposure to an acidic stimulus, numerous Cu2+ and Hg2+ were released, serving as the reporting agent of colorimetric/PEC dual-mode assay. The released Cu2+ and Hg2+ induced localized surface plasmon resonance shifts in Au nanorods and triangular Ag nanoplates through an etching process, respectively, enabling visual analysis of ARGs with distinguishing color changes. Meanwhile, numerous Cu2+ and Hg2+ triggered the amplified PEC variations via reacting with the photoactive layers of CuS/CdS and ZnS, respectively. Thus, a rapid and ultrasensitive colorimetric/PEC dual-mode detection of multiple ARGs was achieved with the detection limit down to 17.2 aM. Furthermore, such dual-mode bioassay could discriminate single-base mismatch and successfully determine ARGs in E. coli plasmids and sludge samples, holding great promise for point-of-care genetic diagnostics.

Aptamer tuned nanozyme activity of nickel-metal-organic framework for sensitive electrochemical aptasensing of tetracycline residue

It is urgently needed to develop high-performance method for tetracycline (TC) analysis to meet the growing concerns about food safety. Herein, a MOF of Ni2+-2,3,6,7,10,11-hexahydroxytriphenylene (Ni-HHTP) with peroxidase activity has been prepared and coated on a screen printing electrode, followed by non-covalent adsorption of tetracycline aptamer (TC-Apt) through the π-stacking. The spectroscopic and electrochemical assays show that TC-Apt can effectively enhance the nanozyme activity of Ni-HHTP using 3,3',5,5'-tetramethylbenzidine (TMB)/H2O2 as the probe. Upon binding with TC, the configuration of TC-Apt is changed and desorbs from the Ni-HHTP, resulting in the decrease of the nanozyme activity of aptasensor. Based on this principle, the target TC can be analyzed in concentrations ranging from 10 pM to 1.0 μM, with a detection limit of 1.9 pM. The aptsensor is also applicable for TC analysis in fresh Ctenopharyngodon idella meat and milk, which provides a new approach for TC residue monitoring in food.

MOF-based nanocomposites as transduction matrices for optical and electrochemical sensing

Metal Organic Frameworks (MOFs), a class of crystalline microporous materials have been into research limelight lately due to their commendable physio-chemical properties and easy fabrication methods. They have enormous surface area which can be a working ground for innumerable molecule adhesions and site for potential sensor matrices. Their biocompatibility makes them valuable for in vitro detection systems but a compromised conductivity requires a lot of surface engineering of these molecules for their usage in electrochemical biosensors. However, they are not just restricted to a single type of transduction system rather can also be modified to achieve feat as optical (colorimetry, luminescence) and electro-luminescent biosensors. This review emphasizes on recent advancements in the area of MOF-based biosensors with focus on various MOF synthesis methods and their general properties along with selective attention to electrochemical, optical and opto-electrochemical hybrid biosensors. It also summarizes MOF-based biosensors for monitoring free radicals, metal ions, small molecules, macromolecules and cells in a wide range of real matrices. Extensive tables have been included for understanding recent trends in the field of MOF-composite probe fabrication. The article sums up the future scope of these materials in the field of biosensors and enlightens the reader with recent trends for future research scope.

Metal Porphyrin Complex Combined with Polymerization and Isomerization Cyclic Amplification for a Sensitive Photoelectrochemical Assay

5,10,15,20-Tetrakis(4-aminophenyl)-21H,23H-porphine (TPAPP) possesses good light-harvesting ability and photoelectrochemical (PEC) cathode response signal; however, the disadvantages of easy stacking and weak hydrophilicity limit its application as a signal probe in PEC biosensors. Based on these, we prepared a Fe³⁺ and Cu²⁺ co-coordinating photoactive material (TPAPP-Fe/Cu) with horseradish peroxidase (HRP)-like activity. The metal ions in the porphyrin center not only enabled the directional flow of photogenerated electrons between electron-rich porphyrin and positive metal ions within inner-/intermolecular layers but also accelerated electron transfer through a synergistic redox reaction of Fe(III)/Fe(II) and Cu(II)/Cu(I) as well as rapid generation of superoxide anion radicals (O₂^-•) by mimicking catalytically produced and dissolved oxygen, thereby providing the desired cathode photoactive material with extremely high photoelectric conversion efficiency. Accordingly, by combining with toehold-mediated strand displacement (TSD)-induced single cycle and polymerization and isomerization cyclic amplification (PICA), an ultrasensitive PEC biosensor was constructed for the detection of colon cancer-related miRNA-182-5p. The ultratrace target could be converted to abundant output DNA by TSD possessing the desirable amplifying ability to trigger PICA for forming long ssDNA with repetitive sequences, thus decorating substantial TPAPP-Fe/Cu-labeled DNA signal probes for producing high PEC photocurrent. Meanwhile, the Mn(III) meso-tetraphenylporphine chloride (MnPP) was embedded in dsDNA to further exhibit a sensitization effect toward TPAPP-Fe/Cu and an acceleration effect analogous to that of metal ions in the porphyrin center above. As a result, the proposed biosensor displayed a detection limit as low as 0.2 fM, facilitating the development of high-performance biosensors and showing great potential in early clinical diagnosis.