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G-quadruplex secondary structures are naturally found in genome sequences and play essential roles in regulating a wide variety of important biological processes. Although stabilizing effects of monovalent cations (e.g., K+ and Na+) has been recognized during the past decades, a general and reliable analytical method for accurate characterization of specific interactions of K+/Na+ with G-quartets is still not well established. In the present study, we demonstrate a practical strategy that combined the use of a nanoscale ion emitter, a low-flow drying gas and a volatile salt (trimethylammonium acetate) to almost totally suppress the nonspecific cationic adduction to G-quadruplexes during the ionization process. Our combined strategy takes full advantage of the ultrasmall initial charged droplets when employing a nanoscale ion emitter, the maximum uneven fission of charged droplets under the gentle desolvation conditions, and the effective shielding of the negatively charged phosphate groups by trimethylammonium ions, to eventually producing ions of G-quadruplexes free of non-specific K+/Na+ adduction. For the first time, the accurate binding states as well as the quantitative binding constants between K+/Na+ and G-quadruplexes can be directly obtained even in the presence of tens of millimolar non-volatile salts, which has long been a notorious challenge in mass spectrometry. Accurate binding state between Na + and 24TTG directly obtained by electrospray ionization mass spectrometry using a combined strategy for suppressing nonspecific cationic adduction. [Display omitted] • Combined use of a nanoscale ion emitter, a low-flow drying gas, and TMAA to avoid nonspecific cationic adduction in ESI-MS. • Unambiguous characterization of the pre-exist in-solution specific binding stoichiometry between G4s and K+. • Direct characterization of weak interactions between G4s and Na+ even in tens of millimolar non-volatile salts. • Insights into the topological distinctiveness between G4-K+ and G4-Na+ complexes in terms of their unique binding stoichiometry. [ABSTRACT FROM AUTHOR]

Abstract: The strong interactions between poly(dimethylsiloxane) (PDMS) surface and amino acids result in unavoidable adsorption on channel surface. This paper described a simple method to decrease adsorption of analytes by dynamic coating of the PDMS surface. When nonionic surfactant (Tween 20) was added in running buffer as dynamic modifier, electroosmotic flow (EOF) was well-suppressed. Moreover, arginine (Arg), proline (Pro), histidine (His) and threonine (Thr) were successfully separated within 80s in a 3.7cm long separation channel and then detected with an end-channel amperometric detection mode at a copper electrode. Under the optimal conditions, the linear ranges of Arg, Pro, His and Thr were all from 50 to 600μM with detection limits of 13.6, 15.3, 10.6 and 12.8μM, respectively. The relative standard deviations (R.S.D.s) of run-to-run, day-to-day and chip-to-chip on the coated PDMS/PDMS microchip were all below 2.4%. Tween 20 dynamic coating provides reproducible amino acids separations with good performances. [Copyright &y& Elsevier]

A novel integrated chemiluminescence (CL) flow sensor for the determination of adrenaline and isoprenaline is developed based on the enhancing effect of analytes on CL emission of luminol oxidized by periodate in alkaline solution. The analytical reagents luminol and periodate are immobilized on anion exchange resins, respectively, and packed in a glass tube to construct a reagentless sensor. The proposed sensor allows the determination of adrenaline and isoprenaline over the range from 2.0×10−8 to 1.0×10−5 g ml−1 and 2.0×10−7 to 5.0×10−5 g ml−1, respectively. The detection limits are 7.0×10−9 g ml−1 for adrenaline and 5.0×10−8 g ml−1 for isoprenaline with a relative standard deviation of 1.7% for the 1.0×10−7 g ml−1 adrenaline (n=11) and 2.1% for 1.0×10−6 g ml−1 isoprenaline (n=11). The sample throughput was 60 samples h−1. The sensor has been successfully applied to the determination of adrenaline and isoprenaline in pharmaceutical preparations. [Copyright &y& Elsevier]

Two different glucose biosensors for the amperometric determination of glucose, based on poly(p-chlorophenylamide) (PCPA) and bilayer film of PCPA and Nafion (PCPA/Nafion), are successfully developed. These two biosensors show linear amperometric responses to glucose ranging from 2.0×10−4 to 3.5×10−2 mol l−1 and 5.0×10−4 to 7.5×10−2 mol l−1, respectively, with the same correlation coefficient of 0.9988. Effects of polymerization potential and polymerization time on the performance of enzyme sensors are studied. It is found that PCPA, as a non-conducting polymer, can largely reduce the influence of electroactive interferents. Introduction of inner Nafion membrane not only further eliminates the influence of ascorbic acid on the sensor response but also increases electrode stability. [Copyright &y& Elsevier]

A simple and reliable method based on adsorptive stripping at an electrochemically pretreated glassy carbon electrode (GCE) was proposed for simultaneous or individual determination of guanine and adenine in DNA. The detection sensitivity of guanine and adenine was improved greatly by activating the GCE electrochemically. After accumulation on pretreated GCE at open circuit for 5 min or at the potential of +0.3 V for 120 s, guanine and adenine produced well-defined oxidation peaks at about +0.8 and +1.1 V, respectively in pH 5 phosphate buffer. The detection limit for individual measurement of guanine and adenine was 4.5 ng ml−1 (3×10−8 mol l−1) and 4 ng ml−1 (3×10−8 mol l−1), respectively. Acid-denatured DNA showed two oxidation peaks corresponding to guanine and adenine residues in the same buffer. The proposed method can be used to estimate the guanine and adenine contents in DNA with good selectivity in a linear range of 0.25–5 μg ml−1. [Copyright &y& Elsevier]

Nanoparticle plasmon scattering can provide real-time imaging information on the formation process of noble metal-based nanomaterials. Due to the synergistic effect of the interface between metal and oxide supporting pores, metal nanoparticles (NPs), especially Au NPs, generally exhibit higher catalytic activity on oxide carriers than single-component NPs. Here, we use the dark field scattering microscope to in situ monitor the growth of Au on Cu 2 O surface by oxidation-reduction reactions and the nanostructures could be precisely controlled via the scattering signal. The prepared Cu 2 O/Au nanocomposite has a higher electrocatalytic activity toward Glucose. When being used as a potential biosensor for nonenzyme glucose detection, excellent performance, such as high sensitivity with a detection limit of 4 μM, high selectivity and outstanding stability, was obtained. The scattering imaging strategy is a convenient and universal approach in controllable synthesis of plasmonic heterostructures, and leads to the improvement of electrocatalysts in biosensing. [Display omitted] • The scattering imaging strategy is used to in situ monitor the growth of Au on Cu 2 O surface. • The Cu 2 O/Au nanostructures could be precisely controlled via the scattering signal. • The prepared Cu 2 O/Au nanocomposite has a higher electrocatalytic activity toward Glucose. • The paper provides a convenient approach in controllable synthesis of plasmonic electrocatalysts in biosensing. [ABSTRACT FROM AUTHOR]

Simultaneous recording of action potentials (APs) and neurotransmitter release is highly desirable in living neurons since it provides a complete framework of the physiological and pathological statuses of nerve cells. In this work, we proposed an approach coupling ultra-thin microelectrode array (MEA) with total internal reflection fluorescence microscopy (TIRFM), which served as a powerful platform to visualize both APs and vesicular exocytosis in a neuronal circuit model formed by neuron-like PC12 cells. Taking advantages of fluorescent false neurotransmitter (FFN), the transient neurotransmitter transport down an axon could be visualized with high spatial and temporal resolution. The real-time recording of APs burst and neurotransmitter release induced by hypoxia with MEA/TIRFM platform reveals the relevance of electrical and chemical activities in the neuronal model. The combination of the optical and electrical techniques enables mapping of neuron connectivity in an entire neuronal circuit, which may ultimately lead to deeper understanding of nervous system. An ultra-thin MEA was coupled with TIRFM for simultaneous measurements of action potentials and neurotransmitter release in a neuronal network. Image 1 • A platform based on ultra-thin microelectrode array and total internal reflection fluorescence microscopy is proposed. • The combination of optical and electrical techniques enables completely mapping of neuron connectivity for the first time. • Real-time recording of APs and FFN102 release reveals the relevance of electrical and chemical activities of nerve cells. [ABSTRACT FROM AUTHOR]

Abnormal upregulation of telomerase RNA (TR) is a hallmark event at various stages of tumor progression, providing a universal marker for early diagnosis of cancer. Here, we have developed a triple signal amplification strategy for in situ visualization of TR in living cells, which sequentially incorporated the target-initiated strand displacement circuit, multidirectional rolling circle amplification (RCA), and Mg2+ DNAzyme-mediated amplification. All oligonucleotide probes and cofactors were transfected into cells in one go, and then escaped from lysosomes successfully. Owing to the specific base pairing, the amplification cascades could only be triggered by TR and performed as programmed, resulting in a satisfactory signal-to-background ratio. Especially, the netlike DNA structure generated by RCA encapsulated high concentrations of DNAzyme and substrates (FQS) in a local region, thereby improving the reaction efficiency and kinetics of the third amplification cycle. Under optimal conditions, the proposed method exhibited ultrasensitive detection of TR mimic with a detection limit at pM level. Most importantly, after transfection with the proposed sensing platform, tumor cells can be easily distinguished from normal cells based on TR abundance-related fluorescence signal, providing a new insight into initial cancer screening. Schematic illustration of the triple signal amplification strategy for ultrasensitive in situ imaging of intracellular telomerase RNA. [Display omitted] • A triple signal amplification strategy only triggered by telomerase RNA in living cells was developed. • The netlike DNA structure generated by RCA encapsulated high concentrations of DNAzyme and substrates (FQS) in a local region, thereby improving the reaction efficiency and kinetics of the third amplification cycles. • The proposed method exhibited ultrasensitive detection of telomerase RNA with a detection limit at pM level. • In situ imaging of telomerase RNA in cells and differentiation of tumor cells from normal cells were achieved. [ABSTRACT FROM AUTHOR]

Developing a simple, economical, and accurate diagnostic method has positive practical significance for the early prevention and intervention of Alzheimer's disease (AD). Herein, combining a closed bipolar electrode (BPE) chip with multicolor electrochemiluminescence (ECL) imaging technology, we constructed a low-voltage driven portable visualized ECL device for the early screening of AD. By introducing parallel resistance, the total resistance of the circuit was greatly reduced. A classical mixture of Ir(ppy) 3 and Ru(bpy) 3 2+ was used as multicolor emitters of the anode with TPrA as the co-reactant. Capture of amyloid-β (Aβ) through antigen-antibody recognition, and signal amplification by electroactive covalent organic frameworks (COF) probe at the cathode of BPE caused the significantly increased faradaic current. The electrical balance of the BPE system resulted in the change of the emission color from green to red at the anode. The ECL-BPE sensor shows good reproducibility and high sensitivity with detection limit of 1 pM by naked eye. The driving voltage is 3.0 V, which means the chip could be driven by two fifth batteries. The visualized ECL-BPE sensor provides a promising point-of-care testing (POCT) tool for the screening of Alzheimer's-related diseases in the early stage. Schematic illustration of the ECL-BPE for analysis of Aβ under low driving voltage. [Display omitted] • A low-voltage driven portable multicolor ECL-BPE device was designed for the early screening of AD. • This strategy only requires a parallel resistance with the cathode of the BPE chip, reducing the driving voltage. • The concentration of AD biomarkers can be evaluated by a visually discernible green to yellow to red color change. • The proposed multicolor ECL-BPE chip provides a broad prospect for the development of the next generation of POCT devices. [ABSTRACT FROM AUTHOR]

Herein, a facile and sensitive dual mode sensing strategy for amantadine (AMD) level evaluation by coupling the plasmonic Au nanorod (NR) and supramolecular SH-cyclodextrin (CD) through strong Au-S bond is proposed. Methylene blue (MB) molecules can be inserted into the cavity of CD molecules through the hydrophobic interaction, which would cause the plasmon resonance energy transfer (PRET) process as well as electrochemical signal response due to the spectrum overlap between Au NR and MB molecules and the electrochemical conversion activity of MB molecules. Subsequently, AMD would induce the replacement of MB molecules because of the stronger interaction with CD, resulting the recovery of scattering intensity of Au NR and decrease of the electrooxidation current of MB. On one hand, the increase of Au NR scattering intensity is linearly proportional to AMD with the concentration from 0.4 to 3.0 μM, and reaches a limit of detection (LOD) of 0.28 μM. On the other hand, electrochemical measurement method enlarged the detection range of AMD. The variation of electrochemical oxidation peak current of MB is linearly proportional to the logarithm value of AMD concentration from 2.5 to 375.0 μM, with LOD of 1.9 μM. Subsequently, the proposed dual mode response sensing strategy was successfully employed for the detection of AMD in human serum samples with great selectivity and sensitivity, with a recovery percentage ranged from 92.6 to 112.0%. Overall, this Au NR@SH-CD-MB nanoparticle based single particle plasmonic and electrochemical dual mode sensing method provides great potential in the field of clinical drug detection or metabolic process investigation in the future. Au NR@SH-CD-MB NPs for dual mode AMD detection. [Display omitted] • The CD molecules were introduced for simpler and more effective construction of PRET based plasmonic sensors. • Au NR@SH-CD-MB NPs could produce scattering and electrochemical dual signals for AMD detection. • The prepared Au NR@SH-CD-MB NPs have a good sensitivity and selectivity toward AMD. • The dual signal responsive detection method could achieve a lower LOD and broader dynamic range in biosensing. [ABSTRACT FROM AUTHOR]

In this work, a sensitive and selective detection method based on fluorescence resonance energy transfer (FRET) was developed for analyzing thiol compounds by using a novel fluorescent probe. The new fluorescent probe contains a disulfide bond which selectively reacts with nucleophilic thiolate through the thiol-disulfide exchange reaction. An obvious fluorescence recovery can be observed upon addition of the thiol compound in the fluorescent probe solution due to the thiol-disulfide exchange reaction and the destruction of FRET. This novel probe was successfully used to determine dithiothreitol (DTT), glutathione (GSH) and cysteine (Cys). The limits of detection (LOD) were 2.0 μM for DTT, 0.6 μM for GSH, and 0.8 μM for Cys. This new detection method was further investigated in the analysis of compound amino acid injection. [ABSTRACT FROM AUTHOR]

CRISPR-Cas12a system exhibits tremendous potential in accurate recognition and quantitation of nucleic acids and non-nucleic-acid targets thanks to the discovery of its cleavage capability toward single-stranded DNA (ssDNA). In this study, we developed an efficient electrochemiluminescence (ECL) sensing platform based on CRISPR-Cas12a for the analysis of adenosine triphosphate (ATP). In the presence of the target, the successful release of the DNA activator is specially recognized by Cas12a-crRNA duplex and activates the cleavage of ferrocene (Fc) labeled–ssDNA (Fc-ssDNA) modified on the cathode of bipolar electrode (BPE), resulting in a decrease of ECL intensity of [Ru(bpy) 3 ]2+/TPrA in the anodic cell of BPE. By means of the unique combination of Cas12a with ECL technique based on BPE, it can convert the recognition of target ATP into a detectable ECL signal. The detection limit of ATP was determined to be 0.48 nM under the optimal conditions. This work will expand the application of CRISPR-Cas detection system and propose a potential method for the analysis of non-nucleic-acid targets. Sensing mechanism for ATP detection. [Display omitted] • The paper provides an efficient ECL biosensing system based on CRISPR-Cas12a for the determination of ATP. • CRISPR-Cas12a can convert the recognition of target ATP into detectable ECL signals on bipolar electrodes. • Sensitive quantitative analysis of ATP was achieved with the detection limit of 0.48 nM. [ABSTRACT FROM AUTHOR]

Abstract: The retention factor corresponding to pure water in reversed-phase high performance liquid chromatography (RP-HPLC), k w , was commonly obtained by extrapolation of retention factor (k) in a mixture of organic modifier and water as mobile phase in tedious experiments. In this paper, a relationship between log k w and log k for directly determining k w has been proposed for the first time. With a satisfactory validation, the approach was confirmed to enable easy and accurate evaluation of k w for compounds in question with similar structure to model compounds. Eight PCB congeners with different degree of chlorination were selected as a training set for modeling the log k w −log k correlation on both silica-based C8 and C18 stationary phases to evaluate log k w of sample compounds including seven PCB, six PBB and eight PBDE congeners. These eight model PCBs were subsequently combined with seven structure-similar benzene derivatives possessing reliable experimental K ow values as a whole training set for log K ow −log k w regressions on the two stationary phases. Consequently, the evaluated log k w values of sample compounds were used to determine their log K ow by the derived log K ow −log k w models. The log K ow values obtained by these evaluated log k w were well comparable with those obtained by experimental-extrapolated log k w , demonstrating that the proposed method for log k w evaluation in this present study could be an effective means in lipophilicity study of environmental contaminants with numerous congeners. As a result, log K ow data of many PCBs, PBBs and PBDEs could be offered. These contaminants are considered to widely exist in the environment, but there have been no reliable experimental K ow data available yet. [Copyright &y& Elsevier]

Abstract: We proposed herein a novel approach for fabricating nanoband microelectrodes for electrochemical detection on an electrophoresis microchip. The metal films were first obtained via region-selective electroless deposition of gold or copper films on PDMS substrates by selective region plasma oxidation through shadow masking. Both metal films show uniform surfaces with the thickness at the level of 100nm. By casting another PDMS layer on the metal films, the cross section of the sandwich structures can be used as nanoband microelectrodes, which can be renewed just by cutting. These nanoband microelectrodes are successfully used as electrochemical detectors in microchip electrophoresis for the detection of amino acids, proteins and neurotransmitter molecules. Moreover, integrating an Au-Cu double-metal detector with a double-channel electrophoresis system, we can easily distinguish electroactive amino acids from that of non-electroactive amino acids. [Copyright &y& Elsevier]

Abstract: A novel covalent strategy was developed to modify the poly(dimethylsiloxane) (PDMS) surface. Briefly, dextran was selectively oxidized to aldehyde groups with sodium periodate and subsequently grafted onto amine-functionalized PDMS surface via Schiff base reaction. As expected, the coated PDMS surface efficiently prevented the biomolecules from adsorption. Electro-osmotic flow (EOF) was successfully suppressed compared with that on the native PDMS microchip. Moreover, the stability of EOF was greatly enhanced and the hydrophilicity of PDMS surface was also improved. To apply thus-coated microchip, the separation of peptides, protein and neurotransmitters was investigated in detail. For comparison, these analytes were also measured on the native PDMS microchips. The results demonstrated that these analytes were efficiently separated and detected on the coated PDMS microchips. Furthermore, the relative standard deviations of their migration times for run-to-run, day-to-day, and chip-to-chip reproducibilities were in the range of 0.6–2.7%. In addition, the coated PDMS microchips showed good stability within 1 month. [Copyright &y& Elsevier]

An ascorbic acid (AA) sensor based on an ion-sensitive field-effect transistor (ISFET) was prepared by modifying the sensitive area of the transducer with MnO2 nanoparticles. An additional Nafion membrane coated on top of the sensor was used to immobilize the MnO2 nanoparticles and restrict the amount of ascorbic acid entering the membrane. The reaction of the MnO2 nanoparticles with ascorbic acid produced a local pH change, which was correlated with the ascorbic acid concentration and could be monitored by the ISFET. The linear range of the ascorbic acid sensor was 0.02–1.27 mM, and the detection limit was 0.01 mM. The effects of buffer concentration, pH, and ionic strength on the sensor performance were also examined. In addition, the sensor has good stability and reproducibility, and the construction and renewal of the sensor are simple and inexpensive. [Copyright &y& Elsevier]