Electrochemical Trans-Channel Assay for Efficient Evaluation of Tumor Cell Invasiveness

Ultrasensitive Detection of Matrix Metalloproteinase 2 Activity Using a Ratiometric Surface-Enhanced Raman Scattering Nanosensor with a Core-Satellite Structure

Matrix metalloproteinase 2 (MMP-2) has been considered a promising molecular biomarker for cancer diagnosis due to its related dysregulation. In this work, a core-satellite structure-powered ratiometric surface-enhanced Raman scattering (SERS) nanosensor with high sensitivity and specificity to MMP-2 was developed. The SERS nanosensor was composed of a magnetic bead encapsulated within a 5,5'-dithiobis(2-nitrobenzoic acid) (DTNB)-labeled gold shell as the capture core and a 4-mercaptobenzonitrile (MBN)-encoded silver nanoparticle as the signal satellite, which were connected through a peptide substrate of MMP-2. MMP-2-triggered cleavage of peptides from the core surface resulted in a decrease of the SERS intensity of MBN. Since the SERS intensity of DTNB was used as an internal standard, the reliable and sensitive quantification of MMP-2 activity would be realized by the ratiometric SERS signal, with a limit of detection as low as 2.067 ng/mL and a dynamic range from 5 to 100 ng/mL. Importantly, the nanosensor enabled a precise determination of MMP-2 activity in tumor cell secretions, which may provide an avenue for early diagnosis and classification of malignant tumors.

Graphene Oxide-Mediated Regulation of Volume Exclusion and Wettability in Biomimetic Phosphorylation-Responsive Ionic Gates

Replicating phosphorylation-responsive ionic gates via artificial fluidic systems is essential for biomolecular detection and cellular communication research. However, current approaches to governing the gates primarily rely on volume exclusion or surface charge modulation. To overcome this limitation and enhance ion transport controllability, we introduce graphene oxide (GO) into nanochannel systems, simultaneously regulating the volume exclusion and wettability. Moreover, inspired by (cAMP)-dependent protein kinase A (PKA)-regulated L-type Ca2+ channels, we employ peptides for phosphorylation which preserves them as nanoadhesives to coat nanochannels with GO. The coating boosts steric hindrance and diminishes wettability, creating a substantial ion conduction barrier, which represents a significant advancement in achieving precise ion transport regulation in abiotic nanochannels. Leveraging the mechanism, we also fabricated a sensitive biosensor for PKA activity detection and inhibition exploration. The combined regulation of volume exclusion and wettability offers an appealing strategy for controlled nanofluidic manipulation with promising biomedical applications in diagnosis and drug discovery.

Living electrochemical biosensing: Engineered electroactive bacteria for biosensor development and the emerging trends

Bioelectrical interfaces made of living electroactive bacteria (EAB) provide a unique opportunity to bridge biotic and abiotic systems, enabling the reprogramming of electrochemical biosensing. To develop these biosensors, principles from synthetic biology and electrode materials are being combined to engineer EAB as dynamic and responsive transducers with emerging, programmable functionalities. This review discusses the bioengineering of EAB to design active sensing parts and electrically connective interfaces on electrodes, which can be applied to construct smart electrochemical biosensors. In detail, by revisiting the electron transfer mechanism of electroactive microorganisms, engineering strategies of EAB cells for biotargets recognition, sensing circuit construction, and electrical signal routing, engineered EAB have demonstrated impressive capabilities in designing active sensing elements and developing electrically conductive interfaces on electrodes. Thus, integration of engineered EAB into electrochemical biosensors presents a promising avenue for advancing bioelectronics research. These hybridized systems equipped with engineered EAB can promote the field of electrochemical biosensing, with applications in environmental monitoring, health monitoring, green manufacturing, and other analytical fields. Finally, this review considers the prospects and challenges of the development of EAB-based electrochemical biosensors, identifying potential future applications.

Neuron-Inspired Nanofluidic Biosensors for Highly Sensitive and Selective Imidacloprid Detection

Pesticides have caused concerns about food safety due to their residual effects in vegetables and fruits. Imidacloprid, as the frequently used neonicotinoid pesticide, could harm cardiovascular and respiratory function and cause reproductive toxicity in humans. Therefore, reliable methods for portable, selective, and rapid detection are desirable to develop. Herein, we report a neuron-inspired nanofluidic biosensor based on a tyrosine-modified artificial nanochannel for sensitively detecting imidacloprid. The functional tyrosine is modified on the outer surface of porous anodic aluminum oxide to rapidly capture imidacloprid through π-π interactions and hydrogen bonds. The integrated nanofluidic biosensor has a wide concentration range from 10-8 to 10-4 g/mL with an ultralow detection limit of 6.28 × 10-9 g/mL, which outperforms the state-of-the-art sensors. This work provides a new perspective on detecting imidacloprid residues as well as other hazardous pesticide residues in environmental and food samples.

Solid-State Nanopore/Nanochannel Sensing of Single Entities

Solid-state nanopores/nanochannels, with their high stability, tunable geometry, and controllable surface chemistry, have recently become an important tool for constructing biosensors. Compared with traditional biosensors, biosensors constructed with solid-state nanopores/nanochannels exhibit significant advantages of high sensitivity, high specificity, and high spatiotemporal resolution in the detection single entities (such as single molecules, single particles, and single cells) due to their unique nanoconfined space-induced target enrichment effect. Generally, the solid-state nanopore/nanochannel modification method is the inner wall modification, and the detection principles are the resistive pulse method and the steady-state ion current method. During the detection process, solid-state nanopore/nanochannel is easily blocked by single entities, and interfering substances easily enter the solid-state nanopore/nanochannel to generate interference signals, resulting in inaccurate measurement results. In addition, the problem of low flux in the detection process of solid-state nanopore/nanochannel, these defects limit the application of solid-state nanopore/nanochannel. In this review, we introduce the preparation and functionalization of solid-state nanopore/nanochannel, the research progress in the field of single entities sensing, and the novel sensing strategies on solving the above problems in solid-state nanopore/nanochannel single-entity sensing. At the same time, the challenges and prospects of solid-state nanopore/nanochannel for single-entity electrochemical sensing are also discussed.

In situ peptide self-assembly on ionic nanochannel for dynamic monitoring of MMPs in extracellular matrix

The extracellular matrix (ECM) of tumor mediates malignant transformation and distant metastasis with extracellular proteinases, especially the matrix metalloproteinases (MMPs). However, there is no assay method to trace the dynamic content of MMPs in ECM. In this work, we have proposed a strategy by assembling peptide scaffold on ionic nanochannels to monitor the target proteinases. The short peptide unit is designed to induce self-assembly with good stability, biocompatibility and programmability, while ion nanochannels can provide electrochemical response upon the MMP activities. Taking MMP-2 as an example, the peptide unit includes two regions, one for self-assembly and one for bio-recognition, so the assembly region (KLVFF) can self-assemble to nanofiber networks. In the meantime, since the reactive region (PLGVR) has MMP-2 recognition site, the peptide assembly on nanochannel can thus be used for the detection of active MMP-2 in tumor microenvironment, with a wide linear detection range (10 fg/mL-10 ng/mL) and 6.6 fg/mL limit of detection. Moreover, the availability of the established ECM mimic is able to distinguish active MMP-2 from latent proMMP-2 in tumor samples. By designing different peptide units for self-assembly on the ionic nanochannel, the assay platform can be promisingly used for other proteinases in ECM, so this work may provide a useful approach to trace the dynamic content of the MMPs in tumor microenvironment (TEM).