Engineered Escherichia coli as a Controlled-Release Biocarrier for Electrochemical Immunoassay

Solution-phase nucleic acid reaction weaves interfacial barriers on unmodified electrodes: Just-in-time generation of sensor interface for convenient and highly sensitive bioassays

Electrochemical bioassays that rely on sensor interfaces based on immobilized DNA probes often encounter challenges such as complex fabrication processes and limited binding efficiency. In this study, we developed a novel electrochemical bioassay that bypasses the need for probe immobilization by employing a solution-phase nucleic acid reaction to create interfacial barriers on unmodified electrodes, enabling rapid, just-in-time sensor interface formation. Specifically, a 3'-phosphorylated recognition probe was used to identify the target microRNA-21 (miR-21), followed by target recycling facilitated by duplex-specific nuclease (DSN), which resulted in extensive hydrolysis of the recognition probe into DNA fragments with 3'-hydroxyl ends. These fragments were then extended by terminal deoxynucleotidyl transferase (TdT) to form long poly(A) tails. The extended products hybridized with a thiolated assembly probe rich in thymine bases and subsequently assembled on the unmodified gold electrode (AuE) surface, creating a "barrier effect" that hindered the adsorption of streptavidin-HRP (SA-HRP) on the AuE, generating a detectable electrochemical signal. This method demonstrated excellent analytical performance, with a linear detection range from 10 fM to 10 nM and a detection limit as low as 4.3 fM. Moreover, the assay was successfully applied to detect miR-21 in real biological samples, including cell lines and bladder urothelial carcinoma surgical resection specimens, showing strong concordance with RT-qPCR results. The developed method offers a new approach for establishing electrochemical bioassays without the need for pre-immobilization of probes and with minimal reagent use, presenting a promising tool for clinical diagnostics and cancer research.

Electrochemical Biosensors for Cancer Diagnosis: Multitarget Analysis to Present Molecular Characteristics of Tumor Heterogeneity

Electrochemical biosensors are gaining attention as powerful tools in cancer diagnosis, particularly in liquid biopsy, due to their high efficiency, rapid response, exceptional sensitivity, and specificity. However, the complexity of intra- and intertumor heterogeneity, with variations in genetic and protein expression profiles and epigenetic modifications, makes electrochemical biosensors susceptible to false-positive or false-negative diagnostic outcomes. To address this challenge, there is growing interest in simultaneously analyzing multiple biomarkers to reveal molecular characteristics of tumor heterogeneity for precise cancer diagnosis. In this Perspective, we highlight recent advancements in utilizing electrochemical biosensors for cancer diagnosis, with a specific emphasis on the multitarget analysis of cancer biomarkers including tumor-associated nucleic acids, tumor protein markers, extracellular vesicles, and tumor cells. These biosensors hold significant promise for improving precision in early cancer diagnosis and monitoring, as well as potentially offering new insights into personalized cancer management.

Target-Triggered Aggregation of Modified E. coli for Diagnosis of Ovarian Cancer

Bacteria inherently possess the capability of quorum sensing in response to the environment. In this work, we have proposed a strategy to confer bacteria with the ability to recognize targets with quorum-sensing behavior. Meanwhile, we have successfully achieved artificial control over the target-triggered aggregation of Escherichia coli (E. coli) by modifying the bacteria surface in a new way. Furthermore, by making use of green fluorescent protein (GFP) expressed by E. coli as the output signal, the aggregation of modified E. coli can be observed with the naked eye. Therefore, via the detection of the target, MUC1, an ovarian cancer biomarker, a simple and conveniently operated method to diagnose ovarian cancer is developed in this work. Experimental results show that the developed low-background and enzyme-free amplification method enables the highly sensitive detection of MUC1, achieving a remarkable limit of detection (LOD) of 5.47 fM and a linear detection range spanning from 1 pM to 50 nM and 50 nM to 100 nM, respectively. Clinical samples from healthy donors and patients can give distant assay results, showing great potential for clinical applications of this method.

Controllable Assembly of a Quantum Dot-Based Aptasensor Guided by CRISPR/Cas12a for Direct Measurement of Circulating Tumor Cells in Human Blood

Accurate and sensitive analysis of circulating tumor cells (CTCs) in human blood provides a non-invasive approach for the evaluation of cancer metastasis and early cancer diagnosis. Herein, we demonstrate the controllable assembly of a quantum dot (QD)-based aptasensor guided by CRISPR/Cas12a for direct measurement of CTCs in human blood. We introduce a magnetic bead@activator/recognizer duplex core-shell structure to construct a multifunctional platform for the capture and direct detection of CTCs in human blood, without the need for additional CTC release and re-identification steps. Notably, the introduction of magnetic separation ensures that only a target-induced free activator can initiate the downstream catalysis, efficiently avoiding the undesired catalysis triggered by inappropriate recognition of the activator/recognizer duplex structure by crRNAs. This aptasensor achieves high CTC-capture efficiency (82.72%) and sensitive detection of CTCs with a limit of detection of 2 cells mL-1 in human blood, holding great promise for the liquid biopsy of cancers.

Biohybrid Urchin-Like ZnO-Based Microspheres with Tunable Hierarchical Structures and Enhanced Photoelectrocatalytic Properties

Microorganisms have attracted much attention to act as biotemplates for fabricating micro/nanostructured functional particles. However, it is still challenging to produce tunable hierarchical particles based on microorganisms with intricate architectures and superior stability. Herein, a novel strategy is developed to fabricate biohybrid urchin-like magnetic ZnO microspheres based on Chlorella (Ch.) with tunable hierarchical core-shell structures. Using Ch. cells as microspherical templates, Fe3 O4 nanoparticles and ZnO nanorod (NR) arrays are deposited in sequence to form the final biohybrid heterostructure microspheres (Ch.@Fe3 O4 @ZnO NRs). Ordered growth and structural regulation of 3D ZnO NR arrays are achieved via a facile and controllable manner. Compared with the prepared microspheres with diverse structure configurations of ZnO shells, the Ch.@Fe3 O4 @ZnO NRs possess excellent light absorption and photoelectrocatalysis performance toward tetracycline degradation (normalized apparent rate constant, k = 366.3 h-1 g-1 ), which is significantly larger than that of ZnO nanoflower/nanoparticle loaded types. It also proves that the synergistic enhancement of well-oriented ZnO NR arrays, heterojunction structures, and biomass features is the fundamental reason for outstanding photoelectrocatalytic activity. Due to the remarkable stability and versatility, this work provides abundant opportunities to construct biohybrid multilevel micro/nanostructures with significant potentials for practical applications.

An extracellular electron transfer enhanced electrochemiluminescence aptasensor for Escherichia coli analysis

As a crucial indicator in food and water safety testing, the detection of Escherichia coli plays a significant role in maintaining environmental sanitation and promoting public health. Herein, based on the electrochemical activity characteristics of E. coli, we established an enhanced electrochemiluminescence aptasensor for E. coli analysis. This study presents a new method for accurate identification by utilizing a double aptamer recognition system. Specifically, a nano-cadmium sulfide (CdS) modified aptamer was used for primary labeling, while a second aptamer was immobilized on a graphene/chitosan composite electrode for re-capture. The use of two aptamers improves the accuracy of the identification process. Furthermore, the application of an electrode potential facilitates continuous electron transfer between the electrode and electrochemically active microorganisms, resulting in an enhanced electroluminescence signal in relation to the metabolic status. This strategy possesses better sensitivity, accuracy, and stability, demonstrating its potential for E. coli analysis.