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In this study, a novel all-solid-state ion selective electrode (ASS-ISE) was developed for the detection of Cu2+ by open circuit potential (OCP) based on phytic acid (PA)@Ag, which forms a thin anion layer interacting with positive charged Cu2+. Due to the excellent conductivity and complexing ability with multi-chelating features, PA can selectively recognize metal ions and execute ion-electron conduction. Moreover, with the assistance of Ag nanoparticles, multiple PA molecules were connected, forming a network structure with the improved conductivity and stability. After optimizing the thickness of PA@Ag film, this ASS-ISE gave a near Nernstian behavior (31.3 ± 1.8 mV/dec) towards the variation of Cu2+ concentration in the range of 1.0 × 10−5 to 1.0 × 10−3 mol/L with a detection limit of 2.7 × 10−6 mol/L, and presented excellent selectivity and stability. Furthermore, it was applied in the analysis of Cu2+ in environmental waters with the satisfactory recoveries, and the results were consistent well with those obtained by inductively coupled plasma atomic emission spectrometer, providing a promising alternative for the on-site detection of Cu2+ with simplicity and reliability.

Cigarette smoke contains abundant toxicants, and profiling its cytotoxicity represents a critical topic. In this study, cell-substrate impedance sensing (ECIS) was used to measure the cytotoxicity of 4‑(methylnitrosoamino)‑1‑(3‑pyridinyl)‑1‑butanone (NNK), nicotine, and the total particle material (TPM) of high-tar and low-tar cigarettes on CHO-K1 cells. Normalized impedance values at 3174 Hz were collected with microscopic imaging as an assistant, showing the dynamics of cell damage and the ability for cell self-recovery. The NI determination of the four toxicants indicated that, as the concentration of toxicants increased, cigarette smoke produced more intense toxic effects on the cells, and the ability of cell self-recovery worsened until there was permanent damage to the cells and the cells eventually died. Furthermore, the survival rate of the cells was obtained during treatment. NRU assays as a comparison were developed for evaluating the cytotoxicity by calculating the IC50. Both methods showed that the cytotoxicity decreased in the following order: the TPM of high-tar cigarettes, TPM of low-tar cigarettes, nicotine and NNK. The sensitivity of the ECIS method was higher. Our work provides a useful and convenient approach for determining the cytotoxicity of cigarettes in a real-time, label-free manner, contributing to the development of low-toxicity cigarettes.

In this study, distinguishing skin cancer cells (A431) and normal cells (HaCaT) was achieved using electrical impedance spectroscopy (EIS) with a novel developed device. The proliferation behaviors of the two cell types during a culture period of 5 days were characterized by the normalized impedance measured at 1465 Hz with simultaneous microscopic imaging for assistance. By fitting to the established equivalent circuits, A431 cells generated smaller resistance (Rc) values with smaller increasing variation, and comparable capacitance (Cc) values with similar decreasing variation compared with HaCaT cells. Moreover, Cc values were linearly correlated to the cell number. The results indicate that these two cell types can be distinguished with EIS based on the differences in the values and variation trends of Rc and Cc during the proliferation process in a real-time and label-free manner. Our work supplies a useful analytical approach for skin cancer cell research and may facilitate the early diagnosis of skin cancer.

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.

As a kind of malignant tumor, breast cancer needs more simple and sensitive diagnosis methods. Exosomes, a novel cancer marker, have the potential to be used in cancer biopsy alternative surveillance. Thus, the determination of the correlation between cancer cells and their exosome composition is of significance. Herein, an electrochemiluminescence (ECL) aptasensor has been designed to detect the MUC1 protein expression on breast cancer cells and their derived exosomes. CD63 aptamer was immobilized on the electrode surface to capture the cells and exosomes, and Ru(bpy)32+@SiO2 nanoparticles (Ru@SiO2 NPs) modified with MUC1 aptamer could recognize specifically MUC1 protein on cells and exosomes. The amplified ECL signal from Ru@SiO2 NPs exhibited linear responses in the range of 7.53 - 753 μg/mL with a limit of detection (LOD) of 0.83 μg/mL for MCF-7 cells, as well as linear range of 3.22 × 10−4 - 156 μg/mL with a LOD of 2.73 × 10−4 μg/mL for their exosomes. The expression of MUC1 protein on the surface of MDA-MB-231 and SK-BR-3 cells and their exosomes, were further analyzed, indicating the consistency of MUC1 expression of breast cancer cells and their exosomes. Furthermore, this aptasensor was applied to the determination of MUC1 protein on exosomes in serum samples of patient and normal control, demonstrating its potential for clinical cancer surveillance.

Recently, many strategies have been developed to trace the breast cancer susceptibility gene (BRCA), which is closely related to the occurrence of breast cancer. In this work, a novel recyclable electrochemical sensing platform was constructed to detect BRCA DNA based on the homogeneous hybridization of this target sequence with ferrocene-labeled DNA/Au nanospheres (FcNS) and horseradish peroxidase-labeled DNA/Au nanospheres (HRPNS) concatamers, and the host-guest interaction between cucurbit [7]uril (CB [7]) adsorbed on the electrode and Fc on the hybridization complex. With the optimization of experimental conditions, the fabricated sensing platform showed improved sensitivity with a low detection limit of 25 pM (S/N = 3), contributed by the dual amplification of signal using FcNS and HRPNS concatamers, and high specificity for BRCA DNA. The captured complex was dissociated from CB [7]-modified electrode with the rise of pH value to recycle the sensing platform. Furthermore, this detection strategy displayed the reliability and applicability in the analysis of human serum samples, indicating great potential for applications in early diagnosis of breast cancer.

Amyloid-β oligomers (AβOs) are highly toxic species involved in Alzheimer's disease (AD). Hence, a reliable detection method for AβOs, which are promising potential therapeutic targets and biomarkers for AD, is of great significance for improving the diagnosis of AD. Herein, a novel sandwich assay electrochemical biosensor was developed for highly sensitive and selective detection of AβO, using molecularly imprinted polymers (MIPs) and aptamer as the recognition element. Instead of using an antibody to recognize the AβO target molecules, the AβO in the samples were captured by the film of MIPs and the AβO-specific aptamer, forming a MIPs/target/aptamer sandwich assay for the highly selective detection of AβO. The AβO-specific aptamer was immobilized on the surface of core-shell nanoparticles that combined silver nanoparticles with silica nanoparticles (SiO2@Ag NPs). The highly sensitive electrochemical signal from the sandwich assay was generated by using a small amount of AβO to trigger a large number of electrochemically active Ag NPs. Under the optimized conditions, the developed biosensor showed good linearity in the concentration range of 5 pg mL−1 to 10 ng mL−1 with a limit of detection of 1.22 pg mL−1. The biosensor also showed excellent specificity, reproducibility and stability. In addition, the feasibility of detecting AβO in human serum was successfully verified, demonstrating the promising potential of this approach for clinical research and the early diagnosis of AD.

Exosomes (30–150 nm) secreted by cells play an important role in intercellular communication. Herein, a novel double imprinting-based electrochemical method has been developed for analyzing the particle size distribution (PSD) of mimetic exosomes – a mixture of SiO2@HRP with the diameters in 50 nm, 100 nm and 150 nm at a ratio similar to the exosomes. Double imprinting polymers (DIP) were synthesized with SiO2@HRP at different sizes as template, providing the both recognition of size and morphology. With the capture of the target and the binding of the signal amplification tag – SiO2@Ag/MPBA on the DIP film, a sandwich structure was constructed on Au NPs-GO modified glassy carbon electrode. Under the optimal conditions, the DIP film exhibits the linear correlations between the current intensity and the logarithmic concentration of SiO2@HRP as ΔI50 = −1.52 + 0.50 × lgc50 (2.89 × 104–2.89 × 109 particles/mL), ΔI100 = −1.61 + 0.48 × lgc100 (2.89 × 104–2.89 × 109 particles/mL) and ΔI150 = −1.54 + 0.49 × lgc150 (5.75 × 104–5.75 × 109 particles/mL) with the limit of detection of 1.44 × 103 particles/mL, 5.68 × 102 particles/mL and 7.70 × 102 particles/mL, respectively. Furthermore, the DIP film was applied to the PSD analysis of mimetic exosomes – SiO2@HRP at mixed sizes with a ratio of 50 nm:100 nm:150 nm = 5.0%:42.5%:52.5% detected by nanoparticle tracking analysis (NTA), obtaining a similar result of 50 nm:100 nm:150 nm = 3.6%:43.0%:53.4% with small relative concentration errors. It also exhibited excellent reproducibility and stability. This double imprinting-based method shows high potential in the separation and detection of complex biosamples.

Here, polydopamine derivative monolayer was generated by electro-polymerization of thiol dopamine derivatives modified on gold electrode, and the adhesion of polydopamine made it being a platform for secondary reaction. The influence of pH on formation of polydopamine derivative was investigated. Horseradish peroxidase (HRP) was adhered on the polydopamine derivative monolayer electrode catalyzing the oxidation of H2O2. Cyclic voltammetry (CV) was used to detect the polydopamine monolayer as well as electrochemical catalysis of H2O2. Besides, electrochemical impedance spectroscopy (EIS) and atomic force microscope (AFM) were also employed to characterize the polymeric monolayer.

A palladium nanoparticle/graphene/chitosan/glassy carbon electrode (PdNPs/GR/CS GCE) was prepared and characterized in this paper. This chemical modified electrode displayed excellent eletrochemical catalytic activities towards ascorbic acid (AA), dopamine (DA) and uric acid (UA) compared with bare GCE, PdNPs/GCE and GR/CS GCE by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). All oxidation potentials of AA, DA and UA at the PdNPs/GR/CS GCE shifted negatively and the peak currents were much larger than other electrodes. DPV was used for simultaneous determination of AA, DA and UA in their mixture, and the peak potential separations between AA and DA, DA and UA, AA and UA were 252 mV, 144 mV and 396 mV, respectively. The limits of detection ( S / N = 3) for AA, DA and UA were 20 μM, 0.1 μM and 0.17 μM, respectively. This PdNPs/GR/CS GCE showed many merits in stability, sensitivity, facility and economy.

We use colloidal Au to enhance the DNA immobilization amount on a gold electrode and ultimately lower the detection limit of our electrochemical DNA biosensor. Self-assembly of approximately 16-nm diameter colloidal Au onto a cysteamine modified gold electrode resulted in an easier attachment of an oligonucleotide with a mercaptohexyl group at the 5′-phosphate end, and therefore an increased capacity for nucleic acid detection. Quantitative results showed that the surface densities of oligonucleotides on the Au colloid modified gold electrode were approximately (1–4)×1014 molecules cm−2. Hybridization was induced by exposure of the ssDNA-containing gold electrode to ferrocenecarboxaldehyde labeled complementary ssDNA in solution. The detection limit is 5×10−10 mol l−1 of complementary ssDNA, which is much lower than our previous electrochemical DNA biosensors. The Au nanoparticle films on the Au electrode provide a novel means for ssDNA immobilization and sequence-specific DNA detection.