Toll-like receptor-immobilized carbon paste electrodes with plasma functionalized amine termination: Towards real-time electrochemical based triaging of gram-negative bacteria

Silk-polyurethane composite based flexible electrochemical biosensing platform for pathogen detection

The upcoming era of flexible and wearable electronics necessitates the development of low-cost, flexible, biocompatible substrates amenable to the fabrication of active devices such as electronic devices, sensors and transducers. While natural biopolymers such as Silk are robust and biocompatible, long-term flexibility is a concern due to the inherent brittle nature of soft Silk thin films. This work elucidates the preparation and characterization of Silk-polyurethane (Silk-PU) composite film that provides long-duration flexibility. More importantly, an electrochemical biosensing platform is developed by creating a three-electrode system using a screen-printing technique. The solvents in the Ink had little impact on the film. As a proof of concept, the detection of E. coli, a highly infectious pathogen, was demonstrated using screen-printed electrodes (SPEs) modified with gold nanoparticles. This method effectively detected E. coli across a wide range of concentrations, with a detection limit of 0.12 CFU/mL. The entire surface functionalization and detection process did not impact the Silk-PU substrate. Even after rigorous bending tests, the results were consistent, demonstrating the robustness and flexibility of the Silk-PU film. The platform demonstrated is scalable and amenable for multi-pathogen detection as it not only can integrate several working electrodes, each catering to detection of a particular pathogen, but also serve as a platform for lab-on-chip devices wherein PDMS-based microfluidics can be seamlessly integrated along with the proposed platform.

One-step copper deposition-induced signal amplification for multiplex bacterial infection diagnosis on a lateral flow immunoassay device

The lateral flow immunoassay (LFIA) is predominant in rapid diagnostic tests owing to its cost-effectiveness and operational simplicity. However, the conventional LFIA exhibits limited sensitivity and is susceptible to human variance for the result readout, impacting result interpretation. In this study, we introduced a novel one-step copper deposition-induced signal amplification lateral flow immunoassay (osa-LFIA) that markedly enhances the detection sensitivity for Staphylococcus aureus (protein A) and Pseudomonas aeruginosa (exotoxin A). Utilizing gold nanoparticles (AuNPs) as a catalyst, this approach employs ascorbic acid to reduce Cu2+ to Cu0, depositing on AuNPs at the test line and amplifying the signal. A user-friendly design features a three-dimensional paper structure incorporating pre-dried reagents, enabling a streamlined, efficient testing process. The osa-LFIA significantly lowers detection limits to 3 ng mL-1 for protein A and 10 ng mL-1 for exotoxin A, offering a tenfold improvement over conventional LFIA. Additionally, we developed a portable grayscale detection device, achieving less than 10% error in quantitative analysis compared to the data acquired and analyzed in the lab. This entire process, from detection to signal amplification, is completed in just 20 min. For the clinical trial, we utilized the osa-LFIA to test synovial fluid samples infected with Staphylococcus aureus. We also successfully detected different concentrations of the exotoxin A in parallel, with a recovery value of 96%-110%. Our findings demonstrate the osa-LFIA's potential as a rapid, highly sensitive, and simple-to-use diagnostic tool for detecting various pathogens, significantly advancing the field of rapid diagnostic testing.

Rapid assembly of mixed thiols for toll-like receptor-based electrochemical pathogen sensing

Herein, we describe a rapid and facile fabrication of electrochemical sensors utilizing two different toll-like receptor (TLR) proteins as biorecognition elements to detect bacterial pathogen associated molecular patterns (PAMPs). Using potential-assisted self-assembly, binary mixtures of 11-mercaptoundecanoic acid (MUA) and 6-mercapto-1-hexanol (MCH), or MUA and an in-house synthesized zwitterionic sulfobetaine thiol (DPS) were assembled on a gold working electrode within 5 minutes, which is >200 times shorter than other TLR sensors' preparation time. Electrochemical methods and X-ray photoelectron microscopy were used to characterize the SAM layers. SAMs composed of the betaine terminated thiol exhibited superior resistance to nonspecific interactions, and were used to develop the TLR sensors. Biosensors containing two individually immobilized TLRs (TLR4 and TLR9) were fabricated on separate MUA-DPS SAM modified Au electrodes (MUA-DPS/Au) and tested for their response towards their respective PAMPs. The changes to electron transfer resistance in EIS of the TLR4/MUA-DPS/Au sensor showed a detection limit of 4 ng mL-1 for E. coli 0157:H7 endotoxin (lipopolysaccharide, LPS) and a dynamic range of up to 1000 ng mL-1. The TLR4-based sensor showed negligible response when tested with LPS spiked human plasma samples, showing no interference from the plasma matrix. The TLR9/MUA-DPS/Au sensor responded linearly up to 350 μg mL-1 bacterial DNA, with a detection limit of 7 μg mL-1. The rapid assembly of the TLR sensors, excellent antifouling properties of the mixed SAM assembly, small size and ease of operation of EIS hold great promise for the development of a portable and automated broad-spectrum pathogen detection and classification tool.

Green-Synthesized Amino Carbons for Impedimetric Biosensing of E. coli O157:H7

This study describes the synthesis of amino-functionalized carbon nanoparticles derived from biopolymer chitosan using green synthesis and its application toward ultrasensitive electrochemical immunosensor of highly virulent Escherichia coli O157:H7 (E. coli O157:H7). The inherent advantage of high surface-to-volume ratio and enhanced rate transfer kinetics of nanoparticles is leveraged to push the limit of detection (LOD), without compromising on the selectivity. The prepared carbon nanoparticles were systematically characterized by employing CO2-thermal programmed desorption (CO2-TPD), Fourier transform infrared (FTIR) spectroscopy, X-ray photoelectron spectroscopy (XPS), ultraviolet-visible (UV-visible), and transmission electron microscopy (TEM). The estimated limit of detection of 0.74 CFU/mL and a sensitivity of 5.7 ((ΔRct/Rct)/(CFU/mL))/cm2 in the electrochemical impedance spectroscopy (EIS) affirm the utility of the sensor. The proposed biosensor displayed remarkable selectivity against interfering species, making it well suited for real-time applications. Moreover, the chitosan-derived semiconducting amino-functionalized carbon shows excellent sensitivity in a comparative analysis compared to highly conducting amine-functionalized carbon synthesized via chemical modification, demonstrating its vast potential as an E. coli sensor.