Hollow Prussian blue with ultrafine silver nanoparticle agents (Ag-HPB) integrated sensitive and flexible biosensing platform with highly enzyme loading capability

Herein, the hollow Prussian blue with ultra-small silver nanoparticle agents (Ag-HPB) was prepared by the coating-etching method by applying Prussian blue (PB) coating on Ag nanoparticles (Ag NPs) and diffusing Ag NPs into the PB framework. The flexible biosensing platform based on Ag-HPB nanocomposites incorporated the excellent electrical conductivity of Ag NPs and the superior enzyme loading capacity of the hollow structure, which significantly enhanced its sensing performance. Subsequently, take glucose oxidase (GOx) and acetylcholinesterase (AChE) as examples. The sensing platform displayed a good sensitive response to glucose (Glu) (24.37 μA mM-1 cm-2) and a considerable limit of detection (LOD) for trichlorfon (TCF) as 2.28 pg/mL while exhibiting high stability and good reproducibility. Moreover, it can be applied to monitor trichlorfon in apple samples. Promisingly, the Ag-HPB prepared by the coating-etching strategy provides a reliable strategy for further development of sensitive and flexible biosensing platforms with excellent electrical conductivity and high enzyme loading.

Ultra-thin 2D bimetallic MOF nanosheets for highly sensitive and stable detection of glucose in sweat for dancer

The measurement of glucose concentration in sweat is expected to replace the existing blood glucose detection, which realize the effective way of non-invasive monitoring of human glucose concentration in dancing. High precision glucose detection can be achieved by adjusting the electrode material of the sensor. Thus, in this work, the bimetallic organic frameworks (bi-MOFs) materials containing Mn and Ni ions (NiMn-MOF) with ultrathin nanosheets have been exquisitely designed. The ultrathin nanosheet and heterogeneous metal ions in the structure optimize the electronic structure, which improves the electrical conductivity of MOFs. The success of the preparation strategy leads the good electrocatalytic performance of NiMn-MOF for glucose detection. Detailedly, NiMn-MOF shows high sensitivity of 1576 μA mM-1 cm-2 in the linear range from 0 to 0.205 mM and the wide linear region of 0.255-2.655 mM and 3.655-5.655 mM were also observed. In addition, the high repeatability, reproductivity, long-term stability and ultra-low limited of detection (LOD, 0.28 μM, S/N = 3) provide foundation for the practical sensor application of this NiMn-MOF nanosheets. Remarkably, as designed NiMn-MOF sensor can accurately measure glucose in sweat showing great potential in the field of wearable glucose monitoring during dancing.

Label free flexible electrochemical DNA biosensor for selective detection of Shigella flexneri in real food samples

An effective tool for early-stage selective detection of the foodborne bacterial pathogen Shigella flexneri (S. flexneri) is essential for diagnosing infectious diseases and controlling outbreaks. Here, a label-free electrochemical DNA biosensor for monitoring S. flexneri is developed. To fabricate the biosensor, detection probe (capture probe) is immobilized on the surface of poly melamine (P-Mel) and poly glutamic acid (PGA), and disuccinimidyl suberate (DSS) functionalized flexible indium tin oxide (ITO) electrode. Anthraquinone-2-sulfonic acid monohydrate sodium salt (AQMS) is used as a signal indicator for the detection of S. flexneri. The proposed DNA biosensor exhibits a wide dynamic range with concentration of the targets ranging from 1 × 10^-6 to 1 × 10^-21 molL^-1 with a limit of detection (LOD) of 7.4 × 10^-22 molL^-1 in the complementary linear target of S. flexneri, and a detection range of 8 × 10¹⁰-80 cells/ml with a LOD of 10 cells/ml in real S. flexneri sample. The proposed flexible biosensor provides high specificity for the detection of S. flexneri compared to other target signals such as discrete base mismatches and different bacterial species. The developed biosensor displayed excellent recoveries in detecting S. flexneri in spiked food samples. Therefore, the proposed biosensor can serve as a model methodology for the detection of other pathogens in a broad span of industries.

Flexible triphase enzyme electrode based on hydrophobic porous PVDF membrane for high-performance bioassays

Flexible bioassays based on oxidase-catalyzed and electrocatalytic cascade reactions have been widely reported. However, the fluctuant oxygen level and high anodic potential restricts the detection accuracy. To overcome these challenges, we report here a flexible triphase enzyme electrode by assembling an oxidase enzyme layer and Pt electrocatalysts onto a carbon nanotube film/porous polyvinylidene fluoride hydrophobic substrate. Such a flexible enzyme electrode has an air-liquid-solid triphase reaction zone where oxygen level is air phase dependent (constant and sufficient high), which stabilized the oxidase kinetics and enabled the cathodic measurement of enzymatic product H₂O₂ with minimum interferents caused from oxygen level fluctuation and many oxidizable species in analyte solution. Furthermore, the flexible triphase enzyme electrode exhibited good mechanical stability even after being bent over 600 times and an excellent air permeability, which are crucial to wearable devices that require long-term skin contact.

Flexible sensor based on conducting polymer and gold nanoparticles for electrochemical screening of HPV families in cervical specimens

Considering the low sensitivity of cytological exams and high costs of the molecular methods, the development of diagnostic tests for effective diagnosis of HPV infections is a priority. In this work, biosensor composed of polypyrrole (PPy) films and gold nanoparticles (AuNPs) was obtained for specific detection of HPV genotypes. The biosensor was developed by using flexible electrodes based on polyethylene terephthalate (PET) strips coated with indium tin oxide (ITO). Polymeric films and AuNPs were obtained by electrosynthesis. Oligonucleotides sequences modified with functional amino groups were designed to recognize HPV gene families strictly. The modified oligonucleotides were chemically immobilized on the nanostructured platform. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for the analysis of the electrode modification and monitoring of molecular hybridization. Electrochemical changes were observed after exposure of the biosensors to plasmid samples and cervical specimens. The biosensor based on the BSH16 probe showed a linear concentration range for target HPV16 gene detection of 100 pg μL^-1 to 1 fg μL^-1. A limit of detection (LOD) of 0.89 pg μL^-1 and limit of quantification (LOQ) of 2.70 pg μL^-1 were obtained, with a regression coefficient of 0.98. Screening tests on cervical specimens were performed to evaluate the sensibility and specificity for HPV and its viral family. The expression of a biomarker for tumorigenesis (p53 gene) was also monitored. In this work, a flexible system has been successfully developed for label-free detection of HPV families and p53 gene monitoring with high specificity, selectivity, and sensitivity.

Towards a flexible electrochemical biosensor fabricated from biocompatible Bombyx mori silk

In modern days, there is an increasing relevance of and demand for flexible and biocompatible sensors for in-vivo and epidermal applications. One promising strategy is the implementation of biological (natural) polymers, which offer new opportunities for flexible biosensor devices due to their high biocompatibility and adjustable biodegradability. As a proof-of-concept experiment, a biosensor was fabricated by combining thin- (for Pt working- and counter electrode) and thick-film (for Ag/AgCl quasi-reference electrode) technologies: The biosensor consists of a fully bio-based and biodegradable fibroin substrate derived from silk fibroin of the silkworm Bombyx mori combined with immobilized enzyme glucose oxidase. The flexible glucose biosensor is encapsulated by a biocompatible silicon rubber which is certificated for a safe use onto human skin. Characterization of the sensor set-up is exemplarily demonstrated by glucose measurements in buffer and Ringer's solution, while the stability of the quasi-reference electrode has been investigated versus a commercial Ag/AgCl reference electrode. Repeated bending studies validated the mechanical properties of the electrode structures. The cross-sensitivity of the biosensor against ascorbic acid, noradrenaline and adrenaline was investigated, too. Additionally, biocompatibility and degradation tests of the silk fibroin with and without thin-film platinum electrodes were carried out.

A wearable battery-free wireless and skin-interfaced microfluidics integrated electrochemical sensing patch for on-site biomarkers monitoring in human perspiration

In this study, an ultra-high sensitive, flexible, wireless, battery-free, and fully integrated (no external analysis equipment) electrochemical sensing patch system, including a microfluidic-sweat collecting unit, was newly developed for the on-site monitoring of the [K⁺] concentration in human sweat. Multiwalled carbon nanotube (MWCNT) and MXene-Ti₃C₂T_X based hybrid multi-dimensional networks were applied to obtain a high surface activation area and faster charge transfer rate, strongly adsorbing the valinomycin membrane to protect the ionophore for effective transshipment and immobilization of the [K⁺]. Furthermore, the controllable porosity of carbon-based materials can accelerate the kinetic process of ion diffusion. This hybrid nanonetwork structure effectively enhanced electrochemical stability and sensitivity, addressing the noise and signal drifting problems experienced with low concentration detection. The fabricated sensor exhibited a high ion concentration sensitivity of 63 mV/dec with excellent selectivity, amplified to 173 mV/dec with the integrated amplification system. The Near Field Communication (NFC) is used to transmit measurements to a smartphone wirelessly. A microfluidic channel was integrated with the electrochemical sensor patch to efficiently collect sweat on the human skin surface and mitigate the sensor surface contamination problem. Furthermore, the developed sensing patch can also be applied to other biomarkers on-site detection after modifying the working electrode with the corresponding selective membranes.

Tailoring the Meso-Structure of Gold Nanoparticles in Keratin-Based Activated Carbon Toward High-Performance Flexible Sensor

Flexible biosensors with high accuracy and reliable operation in detecting pH and uric acid levels in body fluids are fabricated using well-engineered metal-doped porous carbon as electrode material. The gold nanoparticles@N-doped carbon in situ are prepared using wool keratin as both a novel carbon precursor and a stabilizer. The conducting electrode material is fabricated at 500 °C under customized parameters, which mimics A-B type (two different repeating units) polymeric material and displays excellent deprotonation performance (pH sensitivity). The obtained pH sensor exhibits high pH sensitivity of 57 mV/pH unit and insignificant relative standard deviation of 0.088%. Conversely, the composite carbon material with sp² structure prepared at 700 °C is doped with nitrogen and gold nanoparticles, which exhibits good conductivity and electrocatalytic activity for uric acid oxidation. The uric acid sensor has linear response over a range of 1-150 µM and a limit of detection 0.1 µM. These results will provide new avenues where biological material will be the best start, which can be useful to target contradictory applications through molecular engineering at mesoscale.