Electrogenerated Chemiluminescence Biosensor Based on Functionalized Two-Dimensional Metal-Organic Frameworks for Bacterial Detection and Antimicrobial Susceptibility Assays

Strand displacement amplification triggered 3D DNA roller assisted CRISPR/Cas12a electrochemiluminescence cascaded signal amplification for sensitive detection of Ec-16S rDNA

BACKGROUND

Escherichia coli can cause gastrointestinal infection, urinary tract infection and other infectious diseases. Accurate detection of Escherichia coli 16S rDNA (Ec-16S rDNA) in clinical practice is of great significance for the identification and treatment of related diseases. At present, there are various types of sensors that can achieve accurate detection of Ec-16S rDNA. Electrochemiluminescence (ECL) has attracted considerable attention from researchers, which causes excellent performance in bioanalysis. Based on the previous research, it is significance to develop a novel, sensitive and efficient ECL biosensor.

RESULTS

In this work, an ECL biosensor for the detection of Ec-16S rDNA was constructed by integrating CRISPR/Cas12a technology with the cascade signal amplification strategy consisting of strand displacement amplification (SDA) and dual-particle three-dimensional (3D) DNA rollers. The amplification products of SDA triggered the operation of the DNA rollers, and the products generated by the DNA rollers activated CRISPR/Cas12a to cleave the signal probe, thereby realizing the change of the ECL signal. The cascade amplification strategy realized the exponential amplification of the target signal and greatly improved the sensitivity. Manganese dioxide nanoflowers (MnO2 NFs) as a co-reaction promoter effectively enhanced the ECL intensity of tin disulfide quantum dots (SnS2 QDs). A new ternary ECL system (SnS2 QDs/S2O82-/MnO2 NFs) was prepared, which made the change of ECL intensity of biosensor more significant. The proposed biosensor had a response range of 100 aM-10 nM and a detection limit of 27.29 aM (S/N = 3).

SIGNIFICANCE AND NOVELTY

Herein, the cascade signal amplification strategy formed by SDA and dual-particle 3D DNA rollers enabled the ECL biosensor to have high sensitivity and low detection limit. At the same time, the cascade signal amplification strategy was integrated with CRISPR/Cas12a to enable the biosensor to efficiently detect the target. It can provide a new idea for the detection of Ec-16S rDNA in disease diagnosis and clinical analysis.

Advances in endotoxin analysis

The outer membrane of gram-negative bacteria is primarily composed of lipopolysaccharide (LPS). In addition to protection, LPS defines the distinct serogroups used to identify bacteria specifically. Furthermore, LPS also act as highly potent stimulators of innate immune cells, a phenomenon essential to understanding pathogen invasion in the body. The complex multi-step process of LPS binding to cells involves several binding partners, including LPS binding protein (LBP), CD14 in both membrane-bound and soluble forms, membrane protein MD-2, and toll-like receptor 4 (TLR4). Once these pathways are activated, pro-inflammatory cytokines are eventually expressed. These binding events are also affected by the presence of monomeric or aggregated LPS. Traditional techniques to detect LPS include the rabbit pyrogen test, the monocyte activation test and Limulus-based tests. Modern approaches are based on protein, antibodies or aptamer binding. Recently, novel techniques including electrochemical methods, HPLC, quartz crystal microbalance (QCM), and molecular imprinting have been developed. These approaches often use nanomaterials such as gold nanoparticles, quantum dots, nanotubes, and magnetic nanoparticles. This chapter reviews current developments in endotoxin detection with a focus on modern novel techniques that use various sensing components, ranging from natural biomolecules to synthetic materials. Highly integrated and miniaturized commercial endotoxin detection devices offer a variety of options as the scientific and technologic revolution proceeds.

Nanomaterials-Enabled Physicochemical Antibacterial Therapeutics: Toward the Antibiotic-Free Disinfections

Bacterial infection continues to be an increasing global health problem with the most widely accepted treatment paradigms restricted to antibiotics. However, the overuse and misuse of antibiotics have triggered multidrug resistance of bacteria, frustrating therapeutic outcomes, and leading to higher mortality rates. Even worse, the tendency of bacteria to form biofilms on living and nonliving surfaces further increases the difficulty in confronting bacteria because the extracellular matrix can act as a robust barrier to prevent the penetration of antibiotics and resist environmental damage. As a result, the inability to eliminate bacteria and biofilms often leads to persistent infection, implant failure, and device damage. Therefore, it is of paramount importance to develop alternative antimicrobial agents while avoiding the generation of bacterial resistance to prevent the large-scale growth of bacterial resistance. In recent years, nano-antibacterial materials have played a vital role in the antibacterial field because of their excellent physical and chemical properties. This review focuses on new physicochemical antibacterial strategies and versatile antibacterial nanomaterials, especially the mechanism and types of 2D antibacterial nanomaterials. In addition, this advanced review provides guidance on the development direction of antibiotic-free disinfections in the antibacterial field in the future.

Dual-channel molecularly imprinted sensor based on dual-potential electrochemiluminescence of Zn-MOFs for double detection of trace chloramphenicol

Functionalized metal organometallic frameworks (MOFs) offer unique advantages in the field of sensing due to their versatility and tunable optical properties. In this work, a new dual-potential electrochemiluminescence (ECL) molecularly imprinted sensor using single Zn-MOF signal probe was designed for double detection of trace chloramphenicol (CAP). As dual-signal ECL emitters, Zn-MOFs were firstly modified on the electrode, showing excellent ECL emission in both cathodic and anodic potential. Then the molecularly imprinted polymer (MIP) was electrochemically prepared using o-phenylenediamine (O-PD) and CAP as a template molecule on the Zn-MOFs/electrode. After CAP as a molecular recognition element was eluted and removed from the Zn-MOFs/MIP/electrode, a new ECL sensor was developed for CAP detection by re-adsorption of CAP on the MIP, resulting in "off" of ECL signal. Compared with the conventional single-signal luminophores, Zn-MOFs show more stable and excellent dual ECL signals, which greatly improve the discriminability and accuracy of CAP trace detection. Under the optimal conditions, the linear range of CAP detection was 1 × 10^-14-1 × 10^-8 M, and the minimum limits of detection (LOD) were 2.1 fM and 2.5 fM for cathode and anode ECL, respectively. This is the first time that Zn-MOFs are used as dual-ECL emitters for molecular sensing systems, and the proposed dual-channel sensing system is flexibly applicable to sensitive detection of other antibiotics, which has broad practical application in food safety.

Color-encoded Escherichia coli assay via enzyme-induced etching of Au@MnO2 nanoparticles

Au@MnO₂ nanoparticles (NPs), as core-shell nanostructures, have been widely used in ions, molecules and enzyme activities detection due to their stable properties and easy preparation, but their application in bacterial pathogens detection is rarely reported. In this work, Au@MnO₂ NPs is employed for Escherichia coli (E. coli) detection through monitoring and measuring β-galactosidase (β-gal) activity based enzyme-induced color-code single particle enumeration (SPE) method. In the existence of E. coli, p-aminophenylβ-D-galactopyranoside (PAPG) can be hydrolyzed to generate p-aminophenol (AP) by the endogenous β-gal of E. coli. MnO₂ shell reacts with AP and produces Mn²⁺, causing the blue shift of the localized surface plasmon resonance (LSPR) peak and color change of the probe from bright yellow to green. With the SPE method, the amount of E. coli can be quantified readily. The detection limit reaches 15 CFU/mL with dynamic range from 100 to 2900 CFU/mL. Besides, this assay is effectively employed to monitor E. coli in river water sample. The designed sensing strategy provides an ultrasensitive and low cost way for E. coli detection and has the possibility to detect other bacteria in environmental monitoring and food quality analysis.

Nanotechnology Approaches for Rapid Detection and Theranostics of Antimicrobial Resistant Bacterial Infections

As declared by WHO, antimicrobial resistance (AMR) is a high priority issue with a pressing need to develop impactful technologies to curb it. The rampant and inappropriate use of antibiotics due to the lack of adequate and timely diagnosis is a leading cause behind AMR evolution. Unfortunately, populations with poor economic status and those residing in densely populated areas are the most affected ones, frequently leading to emergence of AMR pathogens. Classical approaches for AMR diagnostics like phenotypic methods, biochemical assays, and molecular techniques are cumbersome and resource-intensive and involve a long turnaround time to yield confirmatory results. In contrast, recent emergence of nanotechnology-assisted approaches helps to overcome challenges in classical approaches and offer simpler, more sensitive, faster, and more affordable solutions for AMR diagnostics. Nanomaterial platforms (metallic, quantum-dot, carbon-based, upconversion, etc.), nanoparticle-based rapid point-of-care platforms, nano-biosensors (optical, mechanical, electrochemical), microfluidic-assisted devices, and importantly, nanotheranostic devices for diagnostics with treatment of AMR infections are examples of rapidly growing nanotechnology approaches used for AMR management. This review comprehensively summarizes the past 10 years of research progress on nanotechnology approaches for AMR diagnostics and for estimating antimicrobial susceptibility against commonly used antibiotics. This review also highlights several bottlenecks in nanotechnology approaches that need to be addressed prior to considering their translation to clinics.

Two-dimensional metal-organic frameworks: from synthesis to bioapplications

As a typical class of crystalline porous materials, metal-organic framework possesses unique features including versatile functionality, structural and compositional tunability. After being reduced to two-dimension, ultrathin metal-organic framework layers possess more external excellent properties favoring various technological applications. In this review article, the unique structural properties of the ultrathin metal-organic framework nanosheets benefiting from the planar topography were highlighted, involving light transmittance, and electrical conductivity. Moreover, the design strategy and versatile fabrication methodology were summarized covering discussions on their applicability and accessibility, especially for porphyritic metal-organic framework nanosheet. The current achievements in the bioapplications of two-dimensional metal-organic frameworks were presented comprising biocatalysis, biosensor, and theranostic, with an emphasis on reactive oxygen species-based nanomedicine for oncology treatment. Furthermore, current challenges confronting the utilization of two-dimensional metal-organic frameworks and future opportunities in emerging research frontiers were presented.

Hydrogen Bond Organic Frameworks as a Novel Electrochemiluminescence Luminophore: Simple Synthesis and Ultrasensitive Biosensing

Nowadays, continuous efforts have been devoted to searching highly efficient electrochemiluminescence (ECL) emitters for applications in clinical diagnosis and food safety. In this work, triazinyl-based hydrogen bond organic frameworks (Tr-HOFs) were synthesized by N···H hydrogen bond self-assembly aggregation, where 6,6'-(1,4-phenylene)bis(1,3,5-triazine-2,4-diamine) (phenyDAT) was prepared via the cyclization reaction and behaved as a novel ligand. Impressively, the resulting Tr-HOFs showed strong ECL responses with highly enhanced ECL efficiency (21.3%) relative to the Ru(bpy)₃²⁺ standard, while phenyDAT hardly showed any ECL emission in aqueous phase. The Tr-HOFs innovatively worked as a new ECL luminophore to construct a label-free biosensor for assay of kanamycin (Kana). Specifically, the ECL response greatly weakened upon assembly of captured DNA with ferrocene (cDNA-Fc) onto the Tr-HOFs-modified electrode, while the ECL signals were adversely recovered by releasing linked DNA (L-DNA) from double-stranded DNA (dsDNA, hybridization of aptamer DNA (aptDNA) with L-DNA) due to the specific recognition of Kana with the aptDNA combined by the linkage of L-DNA and cDNA-Fc on the electrode. The as-built sensor showed a broadened linear range (1 nM-10 μM) and a limit of detection (LOD) down to 0.28 nM, which also displayed satisfactory results in the analysis of Kana in the milk and diluted human serum samples. This work offers a novel pathway to design an ECL emitter with organic molecules, holding great promise in biomedical analysis and food detection.