Domestic monitoring devices make real-time and long-term health monitoring possible, allowing people to track their health status regularly. Uric acid (UA), creatinine, and urea in urine are three important biomarkers for various diseases, especially kidney diseases. This work proposed a 10-channel potentiometric sensing array containing a UA electrode group, a creatinine electrode group, a urea electrode group, a pH electrode group, and one pair of reference channels, which could be connected with a portable potentiometric analyzer, realizing the simultaneous detection of UA, creatinine, urea, and pH in urine. The prepared Pt/carbon nanotubes (CNTs)-uricase, creatinine deiminase, Au@urease, and polyaniline were employed as the sensing materials, showing responses to four targets with high sensitivity and selectivity. To improve the accuracy of domestic monitoring, a calibration channel was integrated into each electrode group to calibrate the basic potential of the sensing channels, and the influences of pH and temperature on the responses were investigated through the pH electrode group and an external temperature probe to calibrate the slope and intercept. With the preset of the deduced calibration parameters and computational formula for the four targets in the analyzer in Lab Mode, the concentrations of UA, creatinine, and urea and the pH of the human urine samples were directly displayed on the screen of the analyzer in Practical Mode. The agreement of these results with those obtained from commercial kits and pH meters reveals the high potential of these methods for developing domestic devices to facilitate health monitoring.

Intercellular signal transduction plays an important role in the regulation of biological activities. Herein, a Transwell chamber-based two-layer device combined with scanning electrochemical microscopy (SECM) technology has been proposed for in situ investigation of intercellular signal transduction. The cells in the device were cultured on two layers: the lower layer was for signaling cells, and the upper layer was for signal-receiving cells. The extracellular pH (pHe) and ROS (reactive oxygen species, ROSe) were in situ monitored by SECM potentiometric mode and SECM-MPSW (multipotential step waveform), respectively. When the signaling cells, including MCF-7, HeLa, and HFF cells, were electrically stimulated, the ROS release of the signal-receiving cells was promoted. By detecting the pH at the cell surface, it was found that more H+ generated by the signaling cells and two cell layers at a shorter distance could both cause the signal-receiving cells to release more ROS, revealing that H+ is one of the signaling molecules of intercellular communication. This SECM-based in situ monitoring strategy provides an effective way to investigate intercellular signal transduction and explore the corresponding mechanism.

Skin is the first barrier of the immune system, protecting the body from various damages of the external envi-ronment, the signal transduction between skin cells plays an important role in skin healing and injury. Scanning electrochemical microscopy (SECM) combined with a Transwell co-culture device has been proposed to in-situ investigate the signal transduction between skin cells with UVB irradiation, in which, keratinocyte HaCaT cells and fibroblast HFF cells were used as signaling cells and signal-receiving cells, respectively. Extracellular ROS and pH, cell membrane permeability and cell height were in-situ monitored by multi-potential step waveform in SECM (SECM-MPSW), potentiometric mode, shear force mode and the probe approach curve (PAC) combined with COMSOL simulation, respectively. The results revealed that UVB irradiation stimulated HaCaT cells to release excess H+, which diffused to HFF cells and increased the ROS release and membrane permeability with unchanged cell height. Therefore, this work provides an effective way to in-situ investigate intercellular signal transduction.

Home detection of urine is of great significance for health assessment and long-term surveillance of some chronic diseases. However, the most reported sensors require complicated pretreatment of samples or operations, thus limiting their application in home detection. Herein, a self-calibrated potentiometric sensor based on polystyrene-Au nanocomposites has been developed for the determination of Ca2+, consisting of a sensing channel, a calibration channel and a reference channel. By transporting Ca2+ ionophore and ion exchanger into polystyrene nanoparticles, the sensing nanocomposites were synthesized with the functions of target recognition and ion-electron transduction. The construction of the sensor required the modification of the nanocomposites by only drop-casting, which greatly simplified the preparation process and thus increased the stability and reproducibility. Furthermore, the calibration channel provided the same basic potential as the sensing channel in real samples. By subtracting the potential value of calibration channel from that of sensing channel could eliminate the interference of background matrix on target response, thus improving the accuracy of the results in the actual urinalysis. The developed self-calibrated potentiometric sensor showed a near Nernstian response to Ca2+ in a range of $1.0\times 10$ −4 - $1.0\times 10$ −2 M with a slope of 26.3 ± 1.7 mV/decade and intercept of 126.2 ± 5.3 mV and the detection limit is $4.2\times 10$ −5 M. In the application to real urine samples, the results were in good agreement with those obtained by ICP-AES, suggesting this self-calibrated potentiometric Ca2+ in urine and long-term health monitoring.

The expression of potassium channels can be related to the occurrence and development of tumors. Their change would affect K+ outflow. Thus, in situ monitoring of extracellular K+ shows a great significance. Herein, the dual-functional K+ ion-selective electrode as the scanning electrochemical microscopy (SECM) tip (K+-ISE SECM tip) has been developed for in situ monitoring of the extracellular K+. Based on multi-wall carbon nanotubes as a transduction layer, the K+-ISE SECM tip realizes both the plotting of approach curves to position the tip for in situ detection and the recording of potential responses. It shows a near Nernstian response, good selectivity, and excellent stability. Based on these characteristics, it was used to in situ monitor K+ concentrations ([K+]o) of three breast cancer cell lines (MCF-7, MDA-MB-231, and SK-BR-3 cells) at 3 μm above the cell, and [K+]o of MDA-MB-231 cells show the highest value, followed by MCF-7 cells and SK-BR-3 cells. K+ outflow induced by electrical stimulation or pH changes of the culture environment (Δ[K+]o) was further determined, and the possible mechanism of K+ outflow was investigated with 4-aminopyridin (4-AP). MCF-7 cells present the largest value of Δ[K+]o, followed by MDA-MB-231 cells and SK-BR-3 cells at all the stimulation potentials, and pH 6.50 shows the greatest impact on K+ outflow of the three cell lines. The pretreatment of 4-AP changed K+ outflow, probably due to the regulation of voltage-gated channels. These findings provide insight into a deep understanding of the microenvironment influence on K+ outflow, thereby reflecting the possible mechanism of potassium channels.

Reactive oxygen species (ROS) have gained much attention as they are related to cellular homeostasis and functions. New insights into physiology of cancer cells are anticipated from the analysis of their ROS evolution at single cancer cells level. Herein, a novel scanning electrochemical microscopy (SECM) detection strategy with a specifically designed multi-potential step waveform (MPSW) has been developed for in situ monitoring ROS with no interference of dissolved oxygen (DO) at the single cells level. Using MPSW, the signals of three different electrochemical molecules - FcMeOH, DO and ROS could be obtained simultaneously in a single imaging process. Images of FcMeOH were used to determine cell morphology. ROS released by normal and cancer cells without the interference of DO were imaged and quantitatively determined using MPSW. ROS released by cancer cells under different pHs was further investigated, suggesting that an acid environment could stimulate the release of ROS. Thus, this work provides a new way for sensing ROS released by cells without interference, and can be applied in the cancer research based on ROS releasing. (c) 2021 Elsevier Ltd. All rights reserved.

A Faraday-cage-type electrochemical aptasensor based on two-dimensional (2D) nanomaterials was developed for the sensitive detection of Escherichia coli O157:H7. In this electrochemical aptasensor, 2D titanium carbide (Ti3C2Tx) MXene was used for electrode modification. 2D Ti3C2Tx could immobilize aptamers via chelation between titanium and phosphate groups and provide a large electroactive surface for signal transduction. Another 2D zirconium ferrocene-based metal-organic framework (Zr-Fc MOF) combined with gold nanoparticles (AuNPs) and 4-mercaptophenylboronic acid (4-MPBA) (Zr-Fc MOF/AuNPs/4-MPBA) was used as an electrochemical signal label, in which Fc was a signal molecule and AuNPs could improve the electroactivity and combine with 4-MPBA via Au-S bonds. 4-MPBA could bind with E. coli O157:H7 via covalent bonding between boronic acid and the cis-diol of lipopolysaccharides on bacteria cell walls. So, the signal labels could immobilize on the electrode to form a Faraday-cage-type structure owing to the large surface area of Zr-Fc MOF. In this structure, electrons flowed directly between the electrode and ferrocene, and the electrochemical signal could be amplified. When the application of 2D nanomaterials and the Faraday-cage strategy were combined, E. coli O157:H7 was sensitively detected with a detection limit of 3 CFU.mL(-1). The aptasensor was applied for milk sample detection. This aptasensor has practical application potential because of its properties of satisfactory sensitivity, specificity, and stability.

Home potentiometric sensing devices can real-time monitor personal health status and are widely used in the prevention and management of related diseases. However, variations in the composition and the pH of the sample matrix tend to change the basic potential and response slope of some potentiometric sensors, thus affecting detection reliability. Therefore, this work uses the detection of urea in urine as a model to improve reliability of the potentiometric sensor in home detection. Au@urease nanoparticles were synthesized as the sensing material to improve the stability of the urease-based potentiometric sensor. Meanwhile, a multicalibrated urea potential (MCUP) sensing array was designed, which consists of a urea electrode group, a pH electrode group, and a reference channel. The urea electrode group and the pH electrode group contain respectively a sensing channel and a calibration channel. The basic potential of sensing channels can be calibrated through the corresponding calibration channels. Moreover, the pH electrode group can not only measure the pH values of the samples but also calibrate the response slope of the urea electrode group through the calibration coefficient, thus improving the reliability of home detection. Consequently, the potentiometric sensing array based on the enzyme reaction can be applied in body fluids with a wide pH range.

The accurate, simple and sensitive detection of bacterial infections at the early stage is highly valuable in preventing the spread of disease. Recently, CRISPR-Cas12a enzyme-derived nucleic acid detection methods have emerged along with the discovery of the indiscriminate single-stranded DNA (ssDNA) cleavage activity of Cas12a. These nucleic acid detection methods are made effective and sensitive by combining them with isothermal amplification technologies. However, most of the proposed CRISPR-Cas12a strategies involve Cas-crRNA complexes in the preassembled mode, which result in inevitable nonspecific background signals. Besides, the signal ssDNA used in these strategies needs tedious pre-labeling of the signal molecules. Herein, a post-assembly CRISPR-Cas12a method has been proposed based on target-induced transcription amplification and real-time crRNA generation for bacterial 16S rDNA biosensing. This strategy is label-free through the combination of microchip electrophoresis (MCE) detection. In addition, this method eliminates the need for a protospacer adjacent motif (PAM) on the target sequences, and has the potential to be an effective and simple method for nucleic acid detection and infectious disease diagnosis.

All-solid-state potentiometric sensors that are easily miniaturized and arrayed are widely used in home diagnostics. However, changes in sample matrix compositions tend to affect the basic potential of the potentiometric sensor, and pH of sample could change the response slope, thus affecting the detection reliability. This study takes the detection of glucose in urine as a model to increase the reliability of potentiometric sensors in home detection. PtAu/CNTs nanozyme modified by diboronic acid has been designed, showing better catalytic selectivity for glucose by experiments and theoretical calculations. Moreover, glucose electrode group in a multi-calibration glucose potentiometric sensing array can realize the basic potential calibration of sensing channel by the calibration channel. Meanwhile, the pH electrode group can not only measure the urine pH, but also calibrate the response slope of the glucose electrode group, thus improving the reliability of home detection.

The detection of Staphylococcus aureus specific gene in combination with the mecA gene is vitally important for accurate identification of methicillin-resistant Staphylococcus aureus (MRSA). A homogeneous electrochemical DNA sensor was fabricated for simultaneous detection of mecA and nuc gene in MRSA. Metal-organic framework (type UiO-66-NH2) was applied as nanocarrier. Two electroactive dyes, methylene blue (MB) and epirubicin (EP), were encapsulated in UiO-66-NH2, respectively, and were locked by the hybrid double-stranded DNA. Based on the target-response electroactive dye release strategy, once target DNA exists, it completely hybridizes with displacement DNA (DEP and DMB). So DEP and DMB is displaced from the MOF surface, causing the release of electroactive dyes. Co-Zn bimetallic zeolitic imidazolate framework-derived N-doped porous carbon serves for electrode modification to improve electrocatalytic performance and sensitivity. The differential pulse voltammetry peak currents of MB and EP were accurately detected at − 0.14 V and − 0.53 V versus the Ag/AgCl reference electrode, respectively. Under the optimal conditions, the detection limits of mecA gene and nuc gene were 3.7 fM and 1.6 fM, respectively. Combining the effective application of MOFs and the homogeneous detection strategy, the sensor exhibited satisfactory performance for MRSA identification in real samples. The recovery was 92.6–103%, and the relative standard deviation was less than 5%. Besides, MRSA and SA can also be distinguished. This sensor has great potential in practical applications.

Here, an Au-Cu dual-electrode tip was designed to monitor the effect of Cu2+ on the membrane permeability of a single living cell in situ using scanning electrochemical microscopy. The probe approach curves (PACs) were obtained using potassium ferricyanide as a redox mediator. Meanwhile, according to the simulation, theoretical PACs could be acquired. Thus, the cell membrane permeability coefficient (Pm) values were obtained by overlapping the experimental PACs with the theoretical values. Cu2+ was directly generated by electrolyzing the Cu electrode of the dual-electrode tip to investigate its effect on the cell membrane permeability in situ. This work has potential value to improve the understanding of the mechanism of acute heavy metal damage on the cell membrane and will also help clarify the role of heavy metal ions in physiological or pathological processes.

An all-solid-state ion-selective electrode (ASS-ISE) array that is portable and easily miniaturized can meet the needs of home sensing devices for long-term health monitoring. However, their stability and accuracy are affected by the multistep modification required for ASS-ISE manufacturing and the complex background signal of real samples. In this study, a four-channel ISE array with the integration of a calibration channel has been developed based on polystyrene-Au (PS-Au) ion-sensing nanocomposites (PS-Au ISE array) for the home detection of Na+ and K+. The nanocomposites combine target recognition function and ion-electron transduction function and could be modified on the channel surface by direct drop-casting, thus simplifying the preparation process and then improving the stability. Meanwhile, the integrated calibration channel could automatically deduct complex background signals in real sample analysis and thus improve the accuracy. As a result, the proposed self-calibrated PS-Au ISE array showed a near Nernstian behavior for Na+ and K+ in the range of 1 × 10-2 M-1 × 10-4 M, and the detection limits were 6.8 × 10-5 M and 5.5 × 10-5 M in artificial urine. The linear equations can be obtained according to the slopes and intercepts of Na+ and K+, and thus, the concentration of the target ions can be directly read out by combining this PS-Au ISE array with the smart electronic device. Furthermore, the detection results of Na+ and K+ in human urine agreed well with those obtained by ICP-AES, suggesting that this proposed self-calibrated PS-Au ISE array is very suitable for home smart sensing devices, facilitating the health monitoring.

Different cells respond differently to environmental stimulation, resulting in different extracellular pH values. Therefore, the pH of the extracellular microenvironment (pHe) is an important manifestation of cell response to the environment. In this study, a pH-selective dual-microelectrode tip was used as the probe tip of a scanning electrochemical microscopy (SECM) instrument to in situ monitor the pHe changes of different cells after being electrically stimulated by the SECM potential method. pHe is the pH at a certain distance from the cells, and the distance is determined by substituting the current measured by the approach curve into a theoretical calculation. A gold microelectrode was used to determine the distance between the dual-microelectrode tip and the cell, and a pH-selective microelectrode was used to measure the pHe. It was found that the pHe value was related to the distance between the pH-measuring electrode and the cell, and different types of cells had different pHe changes after electrical stimulation. Through fluorescent staining with calcein-AM and propidium iodide, it was verified that this phenomenon was caused by changes in the permeability of the cell membrane due to electrical stimulation. In situ monitoring the pHe changes of different cells will be helpful for exploring the response of cells to environmental stimulation and the mechanism of these different responses.

The imaging resolution of scanning electrochemical microscopy (SECM) depends strongly on the tip electrode size and the tip-substrate distance. Herein, etched glass encapsulation was applied to fabricate a gold disk electrode, and the size of the tip electrode was accurately determined from the steady-state limiting current. Referring to the theoretical research carried out by our predecessors, the formula for the imaging resolution was derived, followed by the imaging of gold spots and cells with the prepared microelectrodes of different sizes and with different tip-substrate distances. A depth scan was performed to generate 2D current maps of the gold spot relative to the position of the microelectrode in the x-z plane. Probe approach curves and horizontal sweeps were obtained from one depth scan image by simply extracting vertical and horizontal cross-sectional lines, and further characterized by comparison with simulated curves through modeling of the experimental system. The experimental results were basically consistent with the theory, revealing that the highest imaging resolution can be obtained with the smallest tip electrode when d/a = 1, and when the size of the tip electrode is fixed the smallest tip-substrate distance can give the highest imaging resolution.

Current strand displacement amplification (SDA)-based nucleic acid sensing methods generally rely on a ssDNA template that involves complementary bases to the endonuclease recognition sequence, which has the limitation of detecting only short nucleic acids. Herein, a new SDA method in which the defective T junction structure is first used to support SDA (dT-SDA) was proposed and applied in longer DNA detection. In dT-SDA, an auxiliary probe and a primer were designed to specifically identify the target gene, following the formation of a stable defective T junction structure through proximity hybridization, and the formation of defective T junctions could further trigger cascade SDA cycling to produce numerous ssDNA products. The quantity of these ssDNA products was detected through microchip electrophoresis (MCE) and could be transformed to the concentration of the target gene. Moreover, the applicability of this developed strategy in detecting long genomic DNA was verified by detecting bacterial 16S rDNA. This proposed dT-SDA strategy consumes less time and has satisfactory sensitivity, which has great potential for effective bacterial screening and infection diagnosis.

Integrating silica with organic nanoparticles can generate unique properties.Here pillar[5]arene/silica hybrid vesicles were constructed based on the amphiphilic and rigid properties of pillararenes,as well as the catalytic hydrolysis of tetraethoxysilane.Such vesicles exhibited the high strength of silica and unique molecular recognition of pillararenes,both of which could tune the pH-trigge red release behavior.Furthermore,a rhodamine B derivative with hexyl group（RhB-C6） was synthesized,which can form a complex with the pillar[5]arene.Based on the host-guest interaction and high strength of silica,the hybrid vesicles could load more RhB-C6 and the rhodamine B was released more slowly compared with the organic vesicles.

An all-solid-state potentiometric aptasensor based on signal amplification by polycation has been proposed for the detection of streptomycin. The carboxylated multi-walled carbon nanotubes (CMWCNTs), polyethylenimine (PEI), and the aptamers of streptomycin were assembled successively on the screen-printing carbon electrode surface by Layer-by-Layer (LbL) technique. The streptomycin would specifically bind to the aptamers, leading to the release of aptamers from the modified electrode surface. Thus, the charges of electrode were changed, causing the variation of open circuit potential (OCP). The introduction of polycation - PEI makes the electrode exposing a large amount of positive charges, so it can combine more aptamers to realize signal amplification. Consequently, under the optimal conditions, this aptasensor showed high sensitivity with corresponding linear response ranges of 1.00 χ 10_11 _ 1.00 χ 10_9 M, and a detection limit of 3.43 χ 10_12 M. Moreover, this aptasensor presented good selectivity, reproducibilityand stability. It could be applied to the detection of milk samples, demonstrating the practicability of this aptasensor.

Abnormal glycosylation of exosomal proteins is related to many diseases. However, there is still a lack of convenient and easy methods for the determination of exosomal glycoproteins. In this work, a ratiometric electrochemical sensor based on the recognition of glycoproteins by boronic acid and core-shell nanoparticles of silica-silver (SiO2@Ag) amplified signals was developed for the highly sensitive detection of exosomal glycoproteins. The CD63 aptamer-SiO2-N-(2-((2-aminoethyl)disulfanyl)ethyl) ferrocene carboxamide (FcNHSSNH2) probe was first connected to graphene oxide-cucurbit [7] (GO-CB [7]) modified GCE through host-guest recognition. The CD63 aptamer was employed for the specific capture of exosomes, and the FcNHSSNH2 molecule was used as the internal reference signal of the sensor. The mercaptophenylboronic acid (MPBA) of MPBA-SiO2@Ag probe was used for the identification of exosomes surface glycoproteins. SiO2 nanoparticle has a large specific surface area, which can load a large amount of silver nanoparticles (AgNPs) for electrochemical signal amplification. The results were expressed as the current ratio of AgNPs and FcNHSSNH2. The introduction of the internal reference molecule FcNHSSNH2 could effectively reduce the measurement error caused by the different DNA density of the substrate, and further improve the sensitivity and accuracy of the detection. Under the optimal experimental conditions, this sensor allowed the sensitive detection of exosomal glycoproteins in the range of 4.2 × 102 to 4.2 × 108 particles/μL with a limit of detection (LOD) of 368 particles/μL. Furthermore, the ratiometric electrochemical sensor could be employed for the detection of exosomal glycoproteins in human serum samples, which has a good clinical application prospect.

An electrochemical sensor based on dual functional Cu2+-modified metal–organic framework nanoparticles (Cu2+-NMOFs) for sensitive detection of bacterial lipopolysaccharide (LPS) is reported. Cu2+-NMOFs were prepared and characterized by SEM, EDS, XRD, and XPS. In this LPS sensor, LPS firstly immobilized in gold nanoparticles/reduced graphene oxide by C18 alkane thiol chains, since the LPS can interact with the C18 alkyl chains by strong intermolecular interactions. Then the Cu2+-NMOFs were captured by the anionic groups of the carbohydrate portions of LPS molecules and played a vital role of recognition unit. More importantly, the Cu2+-NMOFs can catalyze dopamine oxidation to generate aminochrome, resulting in a strong electrochemical oxidation signal. The electrochemical sensor based on dual functional Cu2+-NMOFs was investigated by differential pulse voltammetry, and the stripping peak currents of dopamine oxidized to aminochrome were used to monitor the level of LPS. The developed method demonstrated a wide linear range from 0.0015 to 750 ng/mL with a limit of detection of 6.1 × 10−4 ng/mL. The fabricated sensor was applied to detect LPS in mouse blood serum and satisfactory results were achieved. Compared to other detection schemes by using the LPS-binding proteins, peptides, and aptamer, the proposed LPS determination based on the catalytic peroxidase-mimicking NMOFs has some advantages such as good reproducibility, low detection limit, and excellent specificity.