This work presented a point-of-care (POC) photoelectrochemical (PEC) biosensing for the detection of human papillomavirus-16 (HPV-16) on a portable electrochemical detection system by using CRISPR-Cas12a trans-cleaving the G-quadruplex for the biorecognition/amplification and a hollow In2O3-In2S3-modified screen-printed electrode (In2O3-In2S3/SPE) as the photoactive material. G-quadruplexes were capable of biocatalytic precipitation (H2O2-mediated 4-chloro-1-naphthol oxidation) on the In2O3-In2S3/SPE surface, resulting in a weakened photocurrent, but suffered from trans-cleavage when the CRISPR-Cas12a system specifically recognized the analyte. The photocurrent results could be directly observed with the card-sized electrochemical device via a smartphone, which displayed a high-value photocurrent for these positive samples, while a low-value photocurrent for the target-free samples. Such a system exhibited satisfying photocurrent responses toward HPV-16 within a wide working range from 5.0 to 5000 pM and allowed for detection of HPV-16 at a concentration as low as 1.2 pM. The proposed assay provided a smartphone signal readout to enable the rapid screening PEC determination of HPV-16 concentration without sophisticated instruments, thus meeting the requirements of remote areas and resource-limited settings. We envision that combining an efficient biometric PEC sensing platform with a wireless card-sized electrochemical device will enable high-throughput POC diagnostic analysis.

CRISPR-Cas12a-Derived Photoelectrochemical Biosensor for Point-Of-Care Diagnosis of Nucleic Acid.

Flexible wearable sweat sensors allow continuous, real-time, noninvasive detection of sweat analytes, provide insight into human physiology at the molecular level, and have received significant attention for their promising applications in personalized health monitoring. Electrochemical sensors are the best choice for wearable sweat sensors due to their high performance, low cost, miniaturization, and wide applicability. Recent developments in soft microfluidics, multiplexed biosensing, energy harvesting devices, and materials have advanced the compatibility of wearable electrochemical sweat-sensing platforms. In this review, we summarize the potential of sweat for medical detection and methods for sweat stimulation and collection. This paper provides an overview of the components of wearable sweat sensors and recent developments in materials and power supply technologies and highlights some typical sensing platforms for different types of analytes. Finally, the paper ends with a discussion of the challenges and a view of the prospective development of this exciting field. 

/pdf/wearable-and-flexible-electrochemical-sensors-for-sweat-1w820kbe.pdf

Wearable and flexible electrochemical sensors for sweat analysis: a review

MXenes, transition metal carbide and nitrides with graphene-like structures, have received numerous attention since they were synthesized from MAX phases in 2011. As a rising star in 2D material family, MXenes exhibit charming physical and chemical properties. The superiority in 2D flak structure, combined with rich functional groups, endows MXenes abundant tunable performance and also makes them show unique advantages in various fields. Furthermore, the special structural and functional features also make MXenes and MXene-based materials easy to combine with polymer matrices to meet its high-performance requirements in electrical, thermal, mechanical and other fields. Now, a variety of synthetic methods of MXenes have been explored to suit different application, from hydrofluoric acid to fluorinate-containing acid solution and fluorinate-containing salts. Moreover, diverse modification methods were studied based on abundant terminations of MXene, which are also reviewed. In addition, the fabrication method and performances of MXene/polymer composites are also invested to explore the influence of MXenes on the properties of composite materials. Subsequently, the applications of MXene-based polymeric composites with different properties were also reviewed to explore their application prospects. Lastly, based on current development situation of MXenes, the challenges and prospects for the development of MXene/polymer composites are discussed. In view of the splendid performance of MXenes, obviously, it is certain that MXenes would play a vital role in polymer composites and bring considerable prospects for the development of high-performance composite materials.

MXene as emerging nanofillers for high-performance polymer composites: A review

Large-scale, rapid, and inexpensive serological diagnoses of severe acute respiratory syndrome-coronavirus-2 (SARS-CoV-2) are of great interest in reducing virus transmission at the population level; however, their development is greatly plagued by the lack of available point-of-care methods, leading to low detection efficiency. Herein, an ultrasensitive smartphone-based electrochemical immunoassay is reported for rapid (less than 5 min), low-cost, easy-to-implement detection of the SARS-CoV-2 nucleocapsid protein (SARS-CoV-2 N protein). Specifically, the electrochemical immunoassay was fabricated on a screen-printed carbon electrode coated with electrodeposited gold nanoparticles, followed by incubation of anti-N antibody (Ab) and bovine serum albumin as the working electrode. Accompanied by the antigen–antibody reaction between the SARS-CoV-2 N protein and the Ab, the electron transfer between the electroactive species [Fe(CN)6]3–/4– and the electrode surface is disturbed, resulting in reduced square-wave voltammetry currents at 0.075 V versus the Ag/AgCl reference electrode. The proposed immunoassay provided a good linear range with SARS-CoV-2 N protein concentrations within the scope of 0.01–1000 ng/mL (R2 = 0.9992) and the limit of detection down to 2.6 pg/mL. Moreover, the detection data are wirelessly transmitted to the interface of the smartphone, and the corresponding SARS-CoV-2 N protein concentration value is calculated and displayed. Therefore, the proposed portable detection mode offers great potential for self-differential diagnosis of residents, which will greatly facilitate the effective control and large-scale screening of virus transmission in resource-limited areas.

Smartphone-Based Electrochemical Immunoassay for Point-of-Care Detection of SARS-CoV-2 Nucleocapsid Protein

Point-of-care testing (POCT) technology has made major breakthroughs in community medicine and physician office situations, in tandem with the more ubiquitous and intensive usage of highly integrated quick detection equipment for illness diagnosis, personal care, and mobile healthcare. Although the photoelectrochemical (PEC)-based POCT platform offers the benefits of cheap cost and good user engagement, its commercialization is still limited by the photodetection components' downsizing and mobility, among other factors. In this work, a novel highly integrated PEC biosensor aided by piezophototronics to enhance the efficiency of PEC testing was reported for flexible detection of cancer-associated antigens in biological fluids (prostate-specific antigen, PSA, used as an example). Multiple signal enhancement strategies, including a magnetic bead-linked enzyme-linked immune system catalyzing the production of ascorbic acid from the substrate and a piezoelectric-assisted enhancement strategy, were used for sensitive detection of the analyte to be tested in human body fluids. Unlike the electron transfer mechanism in heterojunctions, piezoelectric semiconductors promote the transfer of electrons and holes by generating piezoelectric potentials in the ultrasonic field, thus contributing to the performance of the PEC testbed. Under optimized conditions, the test platform achieves good correspondence for PSA at 0.02-40 ng mL-1. Impressively, the test devices are comparable to or even superior to gold standard ELISA kits in terms of cost approval and batch testing. This research demonstrates the potential of piezoelectric semiconductors for POC applications in revolutionary PECs and offers innovative thoughts for the development of new PEC bioanalytical components.

Exploiting Photoelectric Activities and Piezoelectric Properties of NaNbO3 Semiconductors for Point-of-Care Immunoassay.

CRISPR-Cas12a-driven MXene-PEDOT:PSS piezoresistive wireless biosensor

Photoelectrochemical immunoassays incorporating specific antigen-antibody recognition reactions with the photon-electron conversion capabilities of photocatalysts have been developed for biomarker detection, but most involve bulky and expensive equipment and are unsuitable for point-of-care testing. Herein, a portable smartphone-based photoelectrochemical immunoassay was innovatively designed for the on-site detection of breast cancer biomarkers (human epidermal growth factor receptor 2; HER2). The system consists of a split-type immunoassay mode, disposable screen-printed electrode covered with hierarchical Co9S8@ZnIn2S4 heterostructures, an integrated circuit board, and a Bluetooth smartphone equipped with a specially designed app. Using alkaline phosphatase (ALP) catalytic strategy to in situ generate ascorbic acid (AA) for electron-donating toward Co9S8@ZnIn2S4 heterostructures, an immunoreaction was successfully constructed for the HER2 detection in the real sample due to the positive correlation of the photocurrent signal to electron donor concentration. Differential charge density indicates that the formation of Co9S8@ZnIn2S4 heterojunction can facilitate the flow of charges in the interface and enhance the photocurrent of the composite. More importantly, the measured photocurrent signal can be wirelessly transmitted to the software and displayed on the smartphone screen to obtain the corresponding HER2 concentration value. The photocurrent values linearly with the logarithm of HER2 concentrations range spanned from 0.01 ng/mL to 10 ng/mL with a detection limit of 3.5 pg/mL. Impressively, the clinical serum specimen results obtained by the proposed method and the wireless sensing device are in good agreement with the enzyme-linked immunosorbent assay (ELISA).

/pdf/smartphone-based-photoelectrochemical-immunoassay-with-co9s8-1tts4ces.pdf

Smartphone-Based Photoelectrochemical Immunoassay with Co9S8@ZnIn2S4 for Point-of-Care Diagnosis of Breast Cancer Biomarker

Taking advantage of the high-efficiency indiscriminate ssDNA cleavage activity of Cas12a in combination with the diffusivity difference of methylene blue (MB)-labeled probes (short oligonucleotides/mononucleotides) toward the negatively-charged indium tin oxide (ITO) electrode, a simple, immobilization-free, highly sensitive, and homogeneous electrochemical biosensor for the detection of human papillomavirus (HPV-16) has been fabricated. At the core of the detection process, Cas12a employed ssDNA trans-cleavage capability to achieve short-strand nucleotide cleavage, while MB-labeled probes served as high-efficiency homogeneous electrochemical emitters to achieve differential pulse voltammetric (DPV) signal. Specifically, due to strong electrostatic repulsion, MB-labeled short oligonucleotides (reporter) cannot diffuse freely to the surface of the negatively charged ITO electrode, and only weak electrochemical signals can be detected. The presence of the target HPV-16 can activate the Cas12a complex to perform indiscriminate ssDNA cleavage of the reporter to produce MB-labeled mononucleotides. The MB-labeled mononucleotides with a smaller size have almost no negative charge, so they very easily diffuse to the surface of the ITO electrode and result in an enhanced electrochemical signal response. Different electrochemical responses (DPV peak intensity) of the CRISPR-Cas12a-assisted amplification strategy can be obtained through the diffusion rate of different MB-labeled DNA on the electrode, which is also positively correlated with the input HPV-16 concentration. Given the unique combination of the CRISPR-Cas12a system with the homogeneous electrochemical solution phase, the detection limit is determined to be 3.22 pM (wide dynamic working range from 0.01 nM to 100 nM) and the two-step detection workflow could be completed within 50 min at ambient temperature, which is superior to that of the HPV-based biosensors previously reported.

An ultrasensitive homogeneous electrochemical biosensor based on CRISPR-Cas12a

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CRISPR-Cas12a-driven MXene-PEDOT:PSS piezoresistive wireless biosensor

Smartphone-Based Electrochemical Immunoassay for Point-of-Care Detection of SARS-CoV-2 Nucleocapsid Protein

Smartphone-Based Photoelectrochemical Immunoassay with Co9S8@ZnIn2S4 for Point-of-Care Diagnosis of Breast Cancer Biomarker

An ultrasensitive homogeneous electrochemical biosensor based on CRISPR-Cas12a