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Inductively coupled plasma-mass spectrometry (ICP-MS) with elemental labeling is a promising strategy for multiplex microRNA (miRNA) analysis. However, it is still challenging for specific analysis of multiple miRNAs with high homology, and the development of multiplex assays is always limited by the complexity of the sequence design. Herein, a simple and direct ICP-MS-based assay was developed for the simultaneous detection of three miRNAs by combining the lanthanide labeling strategy with entropy-driven catalytic (EDC) amplification. Owing to the specificity of EDC for nucleic acid recognition, it is able to differentiate miRNAs with single-base mutation in each EDC circuit. A universal biotin-labeled DNA strand was designed to hybridize with the DNA substrates for three EDC circuits, targeting miRNA-21, miRNA-155, and miRNA-10b, respectively. All the substrates were loaded on the surface of streptavidin magnetic beads. In the presence of target miRNA, the EDC reaction was initiated, and EDC substrates were dissociated, continuously releasing reporter strands that were labeled with lanthanides (Tb/Ho/Lu). After magnetic separation, the supernatant containing the released reporter strands was introduced into an ICP-MS system for simultaneous detection of

Quantification of multiple disease-related microRNAs (miRNAs) is of great significance for clinical diagnosis. Based on the simultaneous multiple element detection ability of inductively coupled plasma-mass spectrometry (ICP-MS) and good specificity of multicomponent nucleic acid enzymes (MNAzymes), a novel and simple method based on the MNAzyme amplification strategy and lanthanide labeling coupled with ICP-MS detection was proposed for the sensitive and simultaneous detection of three miRNAs (miRNA-21, miRNA-155, and miRNA-10b). Specifically, a probe consisting of streptavidin-modified magnetic beads (SA-MBs) and three DNA substrates labeled with lanthanide tags (159Tb/165Ho/175Lu) was constructed. In the presence of target miRNAs, three pairs of MNAzymes were assembled where each pair was hybridized with the corresponding miRNA, and then the substrates on the SA-MBs were cleaved by the activated MNAzymes, continuously releasing the fragment with lanthanide tags. The released lanthanide tags in the supernatant were collected after magnetic separation and analyzed by ICP-MS, realizing the simultaneous quantification of multiple miRNAs. The correlation of the lanthanide tag signal with the miRNA concentration fitted well in a linear model in the range of 50-1000 pmol L-1 (miRNA-21) and 50-2000 pmol L-1 (miRNA-155 and miRNA-10b). The limits of detection for three miRNAs were 11-20 pmol L-1, with the relative standard deviations of 2.2-2.7%. The recoveries of target miRNAs in the human serum and HepG-2 cells were in the range of 87.2-111% and 93.3-111%, respectively. Overall, the method is ideal for the simultaneous quantification of multiple miRNAs with advantages of low spectral interference, high sensitivity, good selectivity, and strong resistance to the complex matrix.

The intensity of electrochemiluminescence (ECL) usually changes rapidly with the progress of the electrochemical process, making it difficult to determine the ECL spectrum with a conventional photomultiplier in a wavelength scan model. Herein, a band-pass filter (BPF)-involved modulating strategy is proposed to upgrade a conventional ECL analyzer to a highly sensitive ECL spectrometer without changing its hardware. The ECL spectrum can be figured out by rapidly and/or continuously modulating a part of the ECL intensity-time curve with a BPF array of different central wavelengths as well as correcting the ECL intensity at different measurement times by a univariate cubic polynomial model. This strategy not only can determine the spectrum of ultra-weak emission with high sensitivity via merely modulating the emission within a short period, including the weak self-ECL from either Ru(bpy)

Detection of biomarkers in body fluids is critical to both diagnosing the life-threatening diseases and optimizing therapeutic interventions. We herein report use of liquid crystals (LCs) to detect biomarkers in blood with high sensitivity and specificity by employing in situ rolling circle amplification (RCA) on magnetic beads (MBs). Specific recognition of cancer biomarkers, such as platelet derived growth factor BB (PDGF-BB) and adenosine, by aptamers leads to formation of a nucleic acid circle on MBs preassembled with ligation DNA, linear padlock DNA, and aptamers, thereby triggering in situ RCA. LCs change from dark to bright appearance after the in situ RCA products being transferred onto the LC interface decorated with octadecy trimethylammonium bromide (OTAB), which is particularly sensitive to the amplified DNA on MBs. Overall, this label-free approach takes advantages of high specificity of aptamer-based assay, efficient enrichment of signaling molecules on MBs, remarkable DNA elongation performance of the RCA reaction, and high sensitivity of LC-based assay. It successfully eliminates the matrix interference on the LC-based sensors and thus achieves at least 4 orders of magnitude improvement in sensitivity for detection of biomarkers compared to other LC-based sensors. In addition, performance of the developed sensor is comparable to that of the commercial ones. Thus, this study provides a simple, powerful, and promising approach to facilitate highly sensitive, specific, and label-free detection of biomarkers in body fluids.

Signal amplification for electrochemiluminescence (ECL) has conventionally been achieved by employing effective matrixes that can accelerate the electrochemical redox processes or carry more electr...

The design and development of novel electrochemiluminescence (ECL) systems with near-infrared (NIR) emission beyond 800 nm are promising for ECL evolution, especially for improving the throughput of the spectrum-resolved multiplexing ECL assay and biological imaging. Herein a biocompatible and environmentally friendly luminophore, that is, the methionine-stabilized Au nanoclusters (Met-Au NCs), are proposed to achieve efficient aqueous ECL of ∼835 nm with triethanolamine as coreactant. The Met-Au NCs not only demonstrate a 75 times enhanced ECL compared with the traditional Au NCs with bovine serum albumin as a capping agent but also can be employed as ECL tags to label proteins with a methionine linker and enable a highly sensitive NIR ECL bioassay. A sandwich-type NIR ECL immunosensor is constructed with the Met-Au NCs as tags and α-fetoprotein (AFP) as a model analyte and exhibits a wide linearity range from 3 fg·mL-1 to 0.1 ng·mL-1 with a limit of detection of 1 fg mL-1 (S/N = 3) as well as desired selectivity.

Signal amplification for electrochemiluminescence (ECL) has conventionally been achieved by employing effective matrixes that can accelerate the electrochemical redox processes or carry more electrochemiluminophores. Herein, a convenient signal-amplification strategy was proposed for an ECL immunoassay with carboxylated g-C

Rapid and accurate determination of H2O2 is of great importance in practical applications. In this study, we demonstrate construction of liquid-crystal (LC)-based sensing platforms for sensitive and real-time detection of H2O2 with high accuracy for the first time. Single-stranded DNA (ssDNA) adsorbed onto the surface of nanoceria is released to the aqueous solution in the presence of H2O2, which disrupts arrangement of the self-assembled cationic surfactant monolayer decorated at the aqueous/LC interface. Thus, the orientation of LCs changes from a homeotropic to planar state, leading to change in the optical response from dark-to-bright appearance. As H2O2 can be produced during oxidation of glucose by glucose oxidase (GOx), detection of glucose is also fulfilled by employing the H2O2 sensing platform. Our system can detect H2O2 and glucose with concentrations as low as 28.9 nM and 0.52 μM, respectively. It shows high promise of using LC-based sensors for the detection of H2O2 and its relevant biomarker...

Quartz crystal microbalance (QCM) is an important tool to detect in real time the mass change at the nanogram level. However, for a QCM operated in the liquid phase, the Sauerbrey equation is usually disturbed by the changes in liquid properties and the longitudinal wave effect. Herein, we report another unfound associated high-frequency resonance (HFR) model for the QCM, with the intensity 2 orders of magnitude higher than that of the fundamental peak in the liquid phase. The HFR model exhibits obvious impact on the response of QCM in the thickness-shear model (TSM), especially for overtones. The frequency of HFR peak is decreased dramatically with increasing conductivity or permittivity of the liquid phase, resulting in considerable additional frequency shifts in the TSM as baseline drift. Compared to that with a faraway HFR peak, the overlapping of HFR peak to a TSM overtone results in the frequency shifts of ±50-70 kHz with its intensity enhancement by 3 orders of magnitude in the later. The HFR behavior is explained by an equivalent circuit model including leading wire inductance, liquid inductance, and static capacitance of QCM. Taking into account the HFR model, the positive frequency shifts of the QCM at high overtones during the cell adhesion process is understandable. Combining the TSM and HFR is an effective way to improve the stability of QCM and provides more reliable information from the responses of QCM. The HFR may have potential application in chemical and biological sensors.

A low-impedance capacitively coupled contactless conductivity detector (LIC (4)D) for microchip capillary electrophoresis was reported. The LIC (4)D was the series combination of a piezoelectric quartz crystal (PQC) resonator with a capacitively coupled contactless conductivity detector (C (4)D) outside on the microchip lid. The electrode impedance in the LIC (4)D was reduced because the capacitive impedance from the wall capacitance was compensated by the inductive impedance from the PQC. The operation frequency of the LIC (4)D was set at the resonant frequency of the series combination of a PQC with a C (4)D, wherein a minimum in the total impedance was obtained. It was shown that the sensitivity of LIC (4)D was much higher than that of C (4)D itself, especially in the microchip with a thick lid. Under the experimental conditions, the signal-to-noise ratios of the LIC (4)D were improved by approximately 20-50 times over those of the C (4)D. Reproducible separations of a mixture of inorganic cations (K (+), Na (+), Li (+)) were demonstrated. After a digital filter treatment by the fast Fourier transform algorithm, the detection limits were 0.38, 0.49, and 1.6 microM for K (+) in the LI C (4)D with the microchip lid thickness of 0.20, 0.40, and 1.0 mm, respectively.