Direct detection of cysteine using functionalized BaTiO3 nanoparticles film based self-powered biosensor

Spherical Nucleic Acids as Modulators of CRISPR/Cas12a by a Steric Barrier Effect for Designing Versatile Biosensors

Discovery of CRISPR/Cas12a has revolutionized broad fields, including gene editing, molecular diagnosis, and biosensing. Flexible regulation of Cas12a activity is important for diverse CRISPR/Cas12a applications, especially for biosensing, but it still faces limitations and challenges. We find gold nanoparticles (AuNPs) modified with a single-stranded DNA activator create a huge steric barrier that strongly locks activators in a one-to-many manner and inhibits Cas12a activity. This finding offers a new way to modulate the activity of Cas12a for applications, such as designing versatile biosensors. We report a spherical nucleic acid (SNA)-modulating CRISPR/Cas12a (SNA-Cas) platform using SNAs as signal translators for target sensing. A stimuli-responsive SNA was constructed by modifying AuNPs with a DNA activator containing a specific trigger element, and the target triggers specific reactions (e.g., thiol-exchange chemical reaction and RNA-cleaving by DNAzymes) to release activators into solution. A free activator initiates trans-cleavage activity of CRISPR/Cas12a, scissoring fluorescent DNA reporters to produce amplified signals. To show proof of concept, we demonstrate SNA-Cas to sensitively detect diverse non-nucleic acid targets, including biological thiol cysteine, heavy metal Pb2+, and biomarkers of O6-methylguanine-DNA-methyltransferases (MGMT) and fat mass and obesity-related protein (FTO) demethylases. This work opens one door for SNA modulating CRISPR/Cas activity and shows great potential in designing versatile biosensors for detecting diverse targets.

Multi-cascade signal amplification and structure modulation strategy for highly sensitive and selective detection of cysteine using bovine serum albumin-stabilized gold nanoflowers as signal mediator

A novel nanosensing system was constructed for highly sensitive and selective detection of cysteine (Cys) via the combination of the excellent optical properties of bovine serum albumin-stabilized gold nanoflowers (BSA-AuNFs), the high selectivity of the molecular structure regulation performance of cystine, and the high sensitivity of the multi-cascade signal amplification strategy. The sensing mechanism has been confirmed by UV-vis absorption spectroscopy, TEM, HRMS and 1H NMR spectra titration analysis, which can effectively improve the sensitivity and selectivity of the detection of Cys. In addition, the molecular structure regulation performance of cystine (disulfide bond effect) further improved the selectivity of this analytical system. Moreover, it is worth noting that the BSA-AuNFs prepared by ultrafast synthesis procedure have a unique spatial structure, which can effectively prevent the interaction with large-sized biothiols (Cys, homocysteine (Hcy), glutathione (GSH)), achieving highly selective detection of Cys in human serum. This is unable to be achieved by using AuNFs prepared via the gold seed method (Gs-AuNFs) as the gold active sites of Gs-AuNFs are completely exposed. These results indicated that the cascade signal amplification sensing strategy with a clear response mechanism has good application prospects in physiological and pathological research.

Applications of Piezoelectric Materials in Biomedical Engineering

Piezoelectric materials are unique biomedical materials whose asymmetric crystal structures enable them to convert various forms of mechanical energy from the environment, including ultrasound, into electrical or chemical energy. These materials have wide applications in the biomedical field and are gradually becoming a research hotspot in applications such as energy harvesters, biosensors, and tissue engineering. This article first provides a systematic review of the research progress on piezoelectric materials, then outlines frontier strategies for achieving high-performance electrical materials and devices. This article discusses the highly oriented nature of piezoelectric materials mediated by intermolecular forces and explores the applications of piezoelectric implants in biomedicine, including biosensing, energy harvesting, tissue engineering, and disease treatment. Finally, the challenges faced by piezoelectric devices in future research are elaborated.

An ALP enzyme-based electrochemical biosensor coated with signal-amplifying BaTiO3 nanoparticles for the detection of an antiviral drug in human blood serum

Tenofovir (TFV) is an antiviral drug used to treat the co-infections of HIV/HBV viruses. Accurate monitoring of TFV drug levels is essential for evaluating patient adherence, optimizing dosage, and assessing treatment efficacy. Herein, we propose an innovative electrochemical sensing approach by using the alkaline phosphatase (ALP) enzyme with the support of BaTiO3 nanoparticles. An attractive sensitivity and selectivity of the developed sensor towards TFV detection were achieved. First, the nanoparticles were synthesized by following a single-step sol-gel method and characterized through various analytical techniques, including SEM, EDX, FT-IR, BET, zeta potential, XRD, and UV-vis and Raman spectroscopy. The suggested mechanism demonstrated the formation of a strong bond between TFV and the ALP enzyme, primarily through the phosphate group, resulting in enzyme inhibition. Various parameters like nanoparticle amount, electrode modification time with enzyme and BaTiO3 nanoparticles, and drug incubation time were optimized. The biosensor demonstrated an outstanding limit of detection (LOD) of 0.09 nM and recovery percentages of 98.6-106% in human blood serum, indicating adequate repeatability and selectivity. The proposed biosensor can be converted into a portable device for measuring small sample volumes and observing patients for immediate medical care or personalized therapies. It achieved better sensitivity compared to existing methods, making it suitable for precise drug detection in microdoses.

From Piezoelectric Nanogenerator to Non-Invasive Medical Sensor: A Review

Piezoelectric nanogenerators (PENGs) not only are able to harvest mechanical energy from the ambient environment or body and convert mechanical signals into electricity but can also inform us about pathophysiological changes and communicate this information using electrical signals, thus acting as medical sensors to provide personalized medical solutions to patients. In this review, we aim to present the latest advances in PENG-based non-invasive sensors for clinical diagnosis and medical treatment. While we begin with the basic principles of PENGs and their applications in energy harvesting, this review focuses on the medical sensing applications of PENGs, including detection mechanisms, material selection, and adaptive design, which are oriented toward disease diagnosis. Considering the non-invasive in vitro application scenario, discussions about the individualized designs that are intended to balance a high performance, durability, comfortability, and skin-friendliness are mainly divided into two types: mechanical sensors and biosensors, according to the key role of piezoelectric effects in disease diagnosis. The shortcomings, challenges, and possible corresponding solutions of PENG-based medical sensing devices are also highlighted, promoting the development of robust, reliable, scalable, and cost-effective medical systems that are helpful for the public.

Intelligent wearable devices based on nanomaterials and nanostructures for healthcare

Emerging classes of flexible electronic sensors as alternatives to conventional rigid sensors offer a powerful set of capabilities for detecting and quantifying physiological and physical signals from human skin in personal healthcare. Unfortunately, the practical applications and commercialization of flexible sensors are generally limited by certain unsatisfactory aspects of their performance, such as biocompatibility, low sensing range, power supply, or single sensory function. This review intends to provide up-to-date literature on wearable devices for smart healthcare. A systematic review is provided, from sensors based on nanomaterials and nanostructures, algorithms, to multifunctional integrated devices with stretchability, self-powered performance, and biocompatibility. Typical electromechanical sensors are investigated with a specific focus on the strategies for constructing high-performance sensors based on nanomaterials and nanostructures. Then, the review emphasizes the importance of tailoring the fabrication techniques in order to improve stretchability, biocompatibility, and self-powered performance. The construction of wearable devices with high integration, high performance, and multi-functionalization for multiparameter healthcare is discussed in depth. Integrating wearable devices with appropriate machine learning algorithms is summarized. After interpretation of the algorithms, intelligent predictions are produced to give instructions or predictions for smart implementations. It is desired that this review will offer guidance for future excellence in flexible wearable sensing technologies and provide insight into commercial wearable sensors.

A gold-silver bimetallic nanocluster-based fluorescent probe for cysteine detection in milk and apple

Noble metal nanoclusters have attracted much attention due to their excellent optical properties. In the present work, a silver-doped gold-based bimetallic nanoclusters (Au/Ag NCs) were reasonably designed and prepared through a one-pot method by using 5-mercapto-1-tetrazolea-acetic acid sodium salt (MTAS) as a protector and capping agent. In comparison with the monometallic nanoclusters, Ag-doped metallic nanoclusters show better performance. The particle size of the MTAS-Au/Ag NCs is slightly larger than that of the undoped Au NCs by about 1.86 ± 0.5 nm, and the MTAS-Au/Ag NCs exhibit an emission peak at 635 nm with a quantum yield (QY) of 3.05%. The presence of cysteine (Cys) induces efficient quenching of the photoluminescence of the obtained Au/Ag NCs, achieving the sensitive detection of Cys with a detection limit of 16 nM. The fluorescence quenching rate of the nano fluorescent probe has a linear relationship with the cysteine concentration. Under the best detection conditions, the linear range for Cys detection with MTAS-Au/Ag NCs as a probe is 0.05-25.0 μM. Moreover, this probe has been successfully applied to the analysis of Cys in milk and apples, and a satisfactory recovery rate has been obtained, indicating the effectiveness and reliability of the sensor system for the detection of actual samples.

Recent Advances in Intelligent Wearable Medical Devices Integrating Biosensing and Drug Delivery

The primary roles of precision medicine are to perform real-time examination, administer on-demand medication, and apply instruments continuously. However, most current therapeutic systems implement these processes separately, leading to treatment interruption and limited recovery in patients. Personalized healthcare and smart medical treatment have greatly promoted research on and development of biosensing and drug-delivery integrated systems, with intelligent wearable medical devices (IWMDs) as typical systems, which have received increasing attention because of their non-invasive and customizable nature. Here, the latest progress in research on IWMDs is reviewed, including their mechanisms of integrating biosensing and on-demand drug delivery. The current challenges and future development directions of IWMDs are also discussed.

Label-Free Sensing of Cysteine through Cadmium Ion Coordination: Smartphone-Based Electrochemical Detection

The detection of biologically important compounds such as cysteine remains a challenge for monitoring body metabolism. This work proposes a transition metal ion coordination-based label-free cysteine sensor with smartphone-based square wave voltammetry sensing system for the point-of-care testing (POCT). In the sensing system, potential excitation and current measurements were accomplished by a miniaturized and integrated circuit board with a smartphone to wirelessly control the system via Bluetooth. The electrochemical currents changed with the cysteine concentrations ranging from 0 μM to 200 μM with a linearity correlation coefficient of 0.9915. The limit of detection was as low as 0.0149 μM for cysteine. The smartphone-based system provides an effective strategy for cysteine detection, and it can also serve as a promising portable sensing platform for the analysis of other small molecules.

Turn-on signal fluorescence sensor based on DNA derived bio-dots/polydopamine nanoparticles for the detection of glutathione

A convenient, fast, sensitive and highly selective fluorescence sensor for the detection of glutathione (GSH) based on DNA derived bio-dots (DNA bio-dots)/polydopamine (PDA) nanoparticles was constructed. The fluorescent switch of DNA bio-dots was induced to turn off because of fluorescence resonance energy transfer (FRET) reactions between DNA bio-dots and PDA. The presence of GSH blocked the spontaneous oxidative polymerization of dopamine (DA) to PDA, leading the fluorescent switch of DNA bio-dots to be "turned on". The degree of fluorescence recovery of DNA bio-dots is linearly correlated with the concentration of GSH within the range of 1.00-100 μmol L-1, and the limit of detection (LOD) is 0.31 μmol L-1 (S/N = 3, n = 9). Furthermore, the fluorescence sensor was successfully used to quantify GSH in human urine and glutathione whitening power, indicating the fluorescence sensor has potential in the detection of human body fluids and pharmaceutical preparations.

Chiral UiO-MOFs based QCM sensors for enantioselective discrimination of hazardous biomolecule

Developments of enantioselective devices for discriminating bio-enantiomers is of significant importance. Due to the vital role of Cysteine (Cys) in biological processes and the hazardous effect of its D-enantiomer, discriminating Cys enantiomers without auxiliary enzyme is highly wanted. In this work, a pair of UiO-MOF enantiomers (UiO-tart) have been fabricated through post-modification, which could be further fabricated into enantiomeric sensing devices (UiO-tart@Au). By employing the Quartz Crystal Microbalance (QCM) technology, gravimetric discrimination of Cys enantiomers could be achieved. UiO-tart@Au is highly enantioselective, and the afforded enantioselective factor (5.97 ± 0.54) represents the best performance reported ever. In the fabricated device, MOF layer acts as the chiral selector for specific Cys enantiomer, and the reaction between the captured Cys enantiomer and Au results in the mass growth of the system. Solid-phase extraction (SPE) gives an e.e. value of 71.6 ± 3.8%, substantially confirming the chiral-selector role of UiO-tart. DFT calculations indicate that enantiomeric H-bonding effect and greater reaction enthalpy should be the reason. To the best of our knowledge, this work represents the first example of chiral tartaric acid derived MOF sensors for enantioselective discrimination of Cys, suggesting a promising potential of developing chiral MOFs based devices for enhanced enantioselective application.

Semiconducting Metal Oxides: SrTiO3, BaTiO3 and BaSrTiO3 in Gas-Sensing Applications: A Review

In this work, a broad overview in the field of strontium titanate (ST, SrTiO3)-, barium titanate (BT, BaTiO3)- and barium strontium titanate (BST, BaSrTiO3)-based gas sensors is presented and discussed. The above-mentioned materials are characterized by a perovskite structure with long-term stability and therefore are very promising materials for commercial gas-sensing applications. Within the last 20 years, the number of papers where ST, BT and BST materials were tested as gas-sensitive materials has ten times increased and therefore an actual review about them in this field has been expected by readers, who are researchers involved in gas-sensing applications and novel materials investigations, as well as industry research and development center members, who are constantly searching for gas-sensing materials exhibiting high 3S parameters (sensitivity, selectivity and stability) that can be adapted for commercial realizations. Finally, the NO2-sensing characteristics of the BST-based gas sensors deposited by the authors with the utilization of magnetron sputtering technology are presented.

Polysaccharides and proteins-based nanogenerator for energy harvesting and sensing: A review

Nanogenerator is a promising energy harvesting device that can scavenge tiny mechanical energy from the surrounding environment, and then convert it into electricity. Natural bio-polymers are the potential candidates for the design of nanogenerators due to their excellent characteristics like piezoelectricity, triboelectricity, non-toxicity, biocompatibility and biodegradability. Especially, nanogenerators using bio-sourced polymers as the core raw materials are suitable for wearable and implantable devices. In this review, major advancements in the sensing field of nanogenerators based on natural polysaccharides and proteins (cellulose, chitosan, alginate, agarose, starch, lignin, silk fibroin, collagen, gelatin, keratin, peptide, M13 bacteriophage, β-cyclodextrin, spider silk, etc.) are summarized. Also, challenges in the improvement of electric output performance, flexibility, anti-humidity and energy management for natural polymers based-nanogenerators are proposed. In the future, they will be applied in daily life as an alternative for traditional power source after addressing issues mentioned above.

An atomic-layer NiO-BaTiO3 nanocomposite for use in electrochemical sensing of serotonin

The NiO films were deposited on the surface of BaTiO₃ (BTO) by atomic layer deposition (ALD). The thickness of NiO film was controlled by the number of ALD cycles, which the optimum number of ALD cycles were 400 cycles. The morphology of NiO-BTO nanocomposite was observed by x-ray diffraction, scanning electron microscope, and transmission electron microscopy. The sensor based on NiO-BTO nanocomposite displays good electrocatalytic activity and high sensitivity for serotonin (at 0.36 V vs. Ag/AgCl). In the range of 0.05-5 μM, the concentrations of serotonin are linearly related to current intensity and the detection limit is 0.03 μM (S/N = 3). The NiO-BTO/GCE was successfully applied in serum samples. It shows that the NiO-BTO nanocomposite prepared by ALD can serve as electrochemical sensor devices and applications in the fields of biosensors.

Coating silver metal-organic frameworks onto nitrogen-doped porous carbons for the electrochemical sensing of cysteine

Nitrogen-doped porous carbons (N-PC) were coated for the first time with silver metal-organic frameworks (Ag-MOF) by the hydrothermal route. The resulted N-PC@Ag-MOF composites present high stability because of the strong interaction between N atoms of N-PC and Ag⁺ ions of Ag-MOF. It was discovered that the electrodes modified with N-PC@Ag-MOF composites display much higher conductivity than the one modified with Ag-MOF. Especially, they provide stable and sharp electrochemical signals of solid-state AgBr at a low potential approaching zero (i.e., 0.02 V), which may aid to overcome the drawback of the traditional electroanalysis at high overpotentials with serious interferences from the samples background. More importantly, the yielded AgBr signals selectively decrease induced by cysteine (Cys) through the specific thiol-bromine replacement reactions that transfer AgBr into non-electroactive Ag-Cys. The proposed method facilitates the selective detection of Cys with two linear working ranges of 0.10 to 100 μM and 100 to 1300 μM, respectively. The N-PC@Ag-MOF-based sensors have been used for detection of spiked Cys in milk samples with good recovery efficiencies. The developed electroanalysis strategy for probing Cys through the specific thiol-bromine replacement has potential applications in the food analysis fields. Ag-MOF was coated onto heteroatoms co-doped porous carbons carriers for the selective electroanalysis strategy for cysteine at the potential approaching zero using Br^- ions.

POMOF/SWNT Nanocomposites with Prominent Peroxidase-Mimicking Activity for l-Cysteine "On-Off Switch" Colorimetric Biosensing

In order to explore novel colorimetric biosensors with high sensibility and selectivity, two new Keggin polyoxometalates (POMs)-based Cu-trz (1,2,4-triazole) metal-organic frameworks (MOFs) with suitable specific surface areas and multiple active sites were favorably fabricated; then single-walled carbon nanotubes (SWNTs) were merged with new POMOFs to construct POMOF/SWNT nanocomposites. Herein, POMOF/SWNT nanocomposites as peroxidase mimics were explored for the first time, and the peroxidase-mimicking activity of the prepared POMOF/SWNT nanocomposites is heavily dependent on the mass ratio of POMOFs and SWNTs, in which the maximum activity is achieved at the mass ratio of 2.5:1 (named PMNT-2). More importantly, PMNT-2 exhibits the lowest limit of detection (0.103 μM) among all reported materials to date and the assumable selectivity toward l-cysteine (l-Cys) detection. With these findings, a convenient, sensitive, and effective "on-off switch" colorimetric platform for l-Cys detection has been successfully developed, providing a promising prospect in the biosensors and clinical diagnosis fields.

A surface plasmon resonance enhanced photoelectrochemical immunoassay based on perovskite metal oxide@gold nanoparticle heterostructures

A visible light-driven photoelectrochemical immunoassay was designed for PSA detection by using perovskite metal oxide@gold nanoparticle heterostructures.

Target-triggered, self-powered DNAzyme–MnO2 nanosystem: towards imaging microRNAs in living cells

We constructed a versatile self-powered DNAzyme–MnO₂ nanosystem for intracellular signal amplification and sensitive imaging of miRNAs in living cells.

FeCo nanoparticles-embedded carbon nanofibers as robust peroxidase mimics for sensitive colorimetric detection of l-cysteine

A simple and low cost detection of l-cysteine is essential in the fields of biosensors and medical diagnosis. In this study, we have developed a simple electrospinning, followed by calcination process to prepare FeCo nanoparticles embedded in carbon nanofibers (FeCo-CNFs) as an efficient peroxidase-like mimic for the detection of l-cysteine. FeCo nanoparticles are uniformly dispersed within CNFs, and their diameters are highly influenced by the calcination temperature. The calcination temperature also influences the peroxidase-like catalytic activity, and the maximum activity is achieved at a calcination temperature of 550 °C. Owing to the high catalytic activity of the as-prepared FeCo-CNFs, a colorimetric technique for the rapid and accurate determination of l-cysteine has been developed. The detection limit is about 0.15 μM with a wide linear range from 1 to 20 μM. In addition, a high selectivity for the detection of l-cysteine over other amino acids, glucose and common ions is achieved. This study provides a simple, rapid and sensitive sensing platform for the detection of l-cysteine, which is a promising candidate for potential applications in biosensing, medicine, environmental monitoring.

Biocompatible Collagen Nanofibrils: An Approach for Sustainable Energy Harvesting and Battery-Free Humidity Sensor Applications

In contrast with the conventional ceramic/oxide humidity sensors (HSs), a self-powered piezoelectric biopolymer HS with reasonable sensitivity, reliability, and a nontoxic and eco-friendly nature is highly desirable. A piezoelectric nanogenerator (PNG)-driven biopolymer-based HS provides a pathway toward a sustainable and greener environment in the field of smart sensors. For that, a piezoelectric collagen nanofibril biopolymer coated on to a cotton fabric has dual functionality (energy harvesting and sensor). Collagen PNG generates a maximum of 45 V/250 nA upon 5 N and can also work as a sensor to measure various percentages of relative humidity (% RH). The HS shows a linear response with a good sensitivity (0.1287 μA/% RH) in the range of 50-90% RH. These results open a field of eco-friendly multifunctional nanomaterials toward the development of noninvasive, implantable smart bio-medical systems.

Laminated Copper Nanocluster Incorporated Antioxidative Paper Device with RGB System-Assisted Signal Improvement

Paper-based analytical devices are an emerging class of lightweight and simple-to-use analytical platform. However, challenges such as instrumental requirements and chemical reagents durability, represent a barrier for less-developed countries and markets. Herein, we report an advanced laminated device using red emitting copper nanocluster and RGB digital analysis for signal improvement. Upon RGB system assistance, the device signal-to-background ratio and the calibration sensitivity are highly enhanced under a filter-free setup. In addition, the calibration sensitivity, limit of detection, and coefficient of determination are on par with those determined by instrumental fluorescence analysis. Moreover, the limitation of using oxidation-susceptible fluorescent nanomaterials is overcome by the introduction of protecting tape barriers, antioxidative sheets, and lamination enclosing. The robustness of device is highly advanced, and the durability is prolonged to more than tenfold.

N-Doped Graphene Quantum Dots-Decorated V2O5 Nanosheet for Fluorescence Turn Off-On Detection of Cysteine

The development of a fast-response sensing technique for detection of cysteine can provide an analytical platform for prescreening of disease. Herein, we have developed a fluorescence turn off-on fluorescence sensing platform by combining nitrogen-doped graphene quantum dots (N-GQDs) with V₂O₅ nanosheets for the sensitive and selective detection of cysteine in human serum samples. V₂O₅ nanosheets with 2-4 layers are successfully synthesized via a simple and scalable liquid exfoliation method and then deposited with 2-8 nm of N-GQDs as the fluorescence turn off-on nanoprobe for effective detection of cysteine in human serum samples. The V₂O₅ nanosheets serve as both fluorescence quencher and cysteine recognizer in the sensing platform. The fluorescence intensity of N-GQDs with quantum yield of 0.34 can be quenched after attachment onto V₂O₅ nanosheets. The addition of cysteine triggers the reduction of V₂O₅ to V⁴⁺ as well as the release of N-GQDs within 4 min, resulting in the recovery of fluorescence intensity for the turn off-on detection of cysteine. The sensing platform exhibits a two-stage linear response to cysteine in the concentration range of 0.1-15 and 15-125 μM at pH 6.5, and the limit of detection is 50 nM. The fluorescence response of N-GQD@V₂O₅ exhibits high selectivity toward cysteine over other 22 electrolytes and biomolecules. Moreover, this promising platform is successfully applied in detection of cysteine in human serum samples with excellent recovery of (95 ± 3.8) - (108 ± 2.4)%. These results clearly demonstrate a newly developed redox reaction-based nanosensing platform using N-GQD@V₂O₅ nanocomposites as the sensing probe for cysteine-associated disease monitoring and diagnosis in biomedical applications, which can open an avenue for the development of high performance and robust sensing probes to detect organic metabolites.