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Herein, we presented a novel logic gate based on an INHIBITION gate that performs parallel readouts. Logic gates performing INHIBITION and YES/OR were constructed using surface-enhanced Raman scattering as optical outputs for the first time. The strategy allowed for simultaneous reading of outputs in one tube. The applicability of this strategy has been successfully exemplified in the construction of half-adder using the two-output logic gates as reporting gates. This reporting strategy provides additional design flexibility for dynamic DNA devices. [ABSTRACT FROM AUTHOR]

Abstract We describe a novel biosensing strategy for sensitive detection of methylamphetamine (MAMP) based on surface enhanced Raman scattering (SERS) by the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled Au@Ag core-shell nanoparticles (Au@Ag). To achieve a favorable SERS substrate, Au@Ag shell-core nanoparticle was synthesized with seeds growth method and well characterized by SEM, TEM and UV–vis spectrometer. The uniform Au@Ag shows an excellent dispersion ability for SERS detection. Under the optimized conditions, the novel biosensor shows a good logarithm linear correlation with the concentration of MAMP ranging from 0.5 ppb to 40 ppb (R2 = 0.986), with a limit of detection at 0.16 ppb of MAMP (3σ). Furthermore, our biosensors hold an excellent selectivity, demonstrated by the negligible interference from the detection of other illicit drugs and metabolites. The concentrations determined with our biosensor from spiked MAMP in human urine sample fell within the same range with the results from mass spectrometry. This indicates that our sensor has a clear potential for the rapid detection of illicit drug in real samples. Graphical abstract fx1 Highlights • Au@Ag core-shell nanoparticles were synthesized and characterized. • A novel SERS sensor was developed for the sensitive detection of methylamphetamine. • Our SERS sensor shows a high sensitivity and selectivity for the detection of methylamphetamine in urine samples. [ABSTRACT FROM AUTHOR]

In this work, we propose for the first time a simple and novel approach based on SERS and As (III) -aptamer for detection of As (III) with excellent selectivity and sensitivity. To maintain the wonderful SERS substrate, Au@Ag shell–core nanoparticle has been successfully synthesized by seeds growth method. As-prepared Au@Ag not only has well-dispersed but also obtains high SERS efficiency. The novel As (III) biosensor has an excellent linear correlation with the concentration of As (III) ranging from 0.5 to 10 ppb. The detection limit of this assay for As (III) is 0.1 ppb (3 times standard deviation rules) which is lower than the maximum limitation guided by the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO). Importantly, the results were demonstrated that no other ions interfered with the detection of As (III) in water. Further, this As (III) biosensor was demonstrated in monitoring As (III) in lake water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Herein, an efficient pair of split G-quadruplex probes was selected (S/N = 21) to construct a simple, rapid and label-free technique for the detections of T4 DNA ligase and PNK activity. DNA ligase and PNK are engaged in DNA replication and repair, ensuring the genetic stability. The detections of T4 ligase and PNK activity are of great significance in biology and biomedicine. Split G-quadruplex probes are robust label-free biosensing tools with turn-on signal readout. The selected pair of split G-quadruplex probes combined with toehold-mediated strand displacement in this work demonstrated an efficient strategy for monitoring the activities of T4 DNA ligase and PNK with good sensitivity. [ABSTRACT FROM AUTHOR]

We describe herein a novel' “turn-on” SERS-based strategy for protease detection based on surface enhanced Raman scattering (SERS) and the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled gold nanoparticles (AuNPs) through enzyme assays. The method employed non-cross-linking aggregation of 4-MBA-modified AuNPs by peptides after treatment with target protease. Thus, SERS signals of 4-MBA are sharply increased because of the decreased electrostatic stability of AuNPs that initiated gold nanoaggregates incorporating Raman reporter molecules due to the formation of “Hot Spots”. Through this strategy, a novel and facile “turn-on” SERS biosensor for trypsin and thrombin based on enzymatic cleavage activity is established with sensitivity, selectivity and simplicity as AuNPs and peptides are easily accessible. Compared with other methods, this newly proposed method has improved sensitivity. The limit of detection was 85 fM (at the ratio of signal to noise, S/N=3:1) for trypsin. Controlled experiments showed that the method exhibited good selectivity over other proteases. We also proved that this principle could be easily adapted to detection of other proteases such as thrombin. The method demonstrated the capability for application in complex matrix samples. The results also presented the potential and superiority of SERS biosensor as a general approach for proteases based on enzyme activity. [ABSTRACT FROM AUTHOR]

In this work, we use for the first time single layer MoS 2 as the fluorescence quencher to design a detection method for Ag + with excellent robustness, selectivity and sensitivity. To maintain the ultrathin MoS 2 , bulk MoS 2 materials have been exfoliated by intercalation with lithium followed by reaction with water. As-prepared two-dimensional MoS 2 not only has good water-solubility but also obtains high fluorescence quenching efficiency within 5 min. Importantly, the detection limit of this assay for Ag + (1 nM) was lower than the maximum limitation guided by the United States Environmental Protection Agency (EPA) and the World Health Organization (WHO). Further, this new Ag + probe was demonstrated in monitoring Ag + in lake water samples with satisfactory results. [ABSTRACT FROM AUTHOR]

Abstract: A facile and label-free assay with label-free molecular beacons (MBs) and fluorescent dye N-methyl mesoporphyrin IX (NMM) was developed for the detection of specific single-stranded DNA sequences. It was demonstrated by a reverse transcription oligonucleotide sequence (target DNA, 20 bases) of RNA fragment of human immunodeficiency virus (HIV) as model systems. In the absence of target DNA, the MBs were in the stem-closed form, the G-quadruplex structure could not form and the fluorescence signal of NMM was very low. In the presence of target DNA the MBs turned “Off” to “On”, thus promoting the formation of G-quadruplex which could greatly enhance the fluorescence of NMM. This biosensor was simple in design, fast in operation, and more convenient and promising than other methods. It took less than 30min to finish and its detection limit was 1.4nM. No sophisticated experimental techniques or chemical modification for DNA sequences were required. This new approach could be widely applied to sensitive and selective nucleic acids detection. [Copyright &y& Elsevier]

Abstract: Herein we describe a novel “turn-off” biosensing strategy for thrombin detection based on Surface Enhanced Raman scattering (SERS) and the mediation of spacing between 4-mercaptobenzoic acid (4-MBA) labeled gold nanoparticles (AuNPs). The multiple arginine peptides that initiated gold nano-aggregates incorporating Raman reporter molecules due to the formation of “Hot Spots”, are induced to disband by the addition of thrombin in which the peptides are catalytically cleaved into fragments and thus SERS signals of 4-MBA are sharply declined because of the weakened ability of fragments to induce aggregation. Through this strategy, a novel “turn-off” SERS biosensor for thrombin based on enzymatic amplification is established with sensitivity, selectivity and simplicity as AuNPs and peptides are easily accessible. Compared with non-enzymatic amplification based methods, this newly proposed method has improved sensitivity. The limit of detection was 160fM (at the ratio of signal to noise, S/N=3:1). Further, controlled experiments showed that the method exhibited good selectivity over other proteases. The method demonstrated the capability and the potential for application in complex matrix and future biomarker development. The results also presented the potential and superiority of SERS biosensor based on signal amplification. [Copyright &y& Elsevier]

Abstract: A selective and sensitive fluorescence biosensor for Ag+ ions and cysteine (Cys) was developed based on the chelation actions between Ag+ ions and guanine bases of G-rich fluorogenic oligonucleotide (FAM-ssDNA) and the different electrostatic affinity between FAM-ssDNA and graphene oxide (GO). FAM-ssDNA adsorbed onto the surface of GO through π–π stacking interaction between the ring structure in the nucleobases and the hexagonal cells of GO, and the fluorescence of the dye was quenched. In the presence of Ag+ ions, the random coil structure changed into a G-Ag+ architecture. As a result, the binding released FAM-ssDNA signal probe from the surface of GO, which disrupted the energy transfer from FAM-ssDNA to GO, recovering the fluorescence emission of FAM-ssDNA. On the other hand, because Cys was a strong Ag+ ions binder, it could deactivate the sensor fluorescence by rewrapping FAM-ssDNA around GO. In this way, these changes in fluorescence intensity allowed the selective detection of Ag+ ions and Cys. [Copyright &y& Elsevier]

Abstract: Enzyme immobilization is one of the key factors in constructing high-performance enzyme biosensors and biofuel cells (BFCs). Herein, we propose a new protocol for efficient immobilization of a glycoprotein enzyme based on the interaction of the 1, 2- or 1, 3-diols in the glycoprotein with a boronic acid functionalized monomer. Briefly, casting a mixture of glucose oxidase (GOx) and anilineboronic acid (ABA) followed by a NaAuCl4 solution to an Au-plated Au electrode surface yielded a GOx–poly(ABA) (PABA)–gold nanoparticle (Aunano) bionanocomposite, and chitosan (CS) was then cast and air-dried. In the present protocol, the small-sized Aunano or Au subnanostructures can form near/on the enzyme molecule, which greatly promotes the electron transfer of enzymatic reaction and enhances the amperometric responses. The thus-prepared CS/GOx–PABA–Aunano/Au-plated Au electrode worked well in the first-/second generation biosensing modes and as a bioanode in a monopolar biofuel cell, with analytical or cell-power performance superior to those of most analogues hitherto reported. [Copyright &y& Elsevier]

Abstract: Acidic amino acids, such as aspartic acid (l-Asp) and glutamic acid, are the primary bioactive molecules of the glycoprotein on the organic/inorganic interface of biomineralized tissues. In this study, the induction of chitosan film modified with l-Asp on the crystal growth of hydroxyapatite (HAP) was investigated by a novel in situ analysis approach, quartz crystal microbalance (QCM), associated with the dynamically structural and morphological characterization of precipitation products on various phases by X-ray diffraction (XRD), Fourier-transformed infrared (FT-IR) spectroscopy and scanning electron microscopy (SEM). The natural chitosan exhibited no inducing ability on the crystal growth of HAP. However, the growth rate of induced HAP was dramatically accelerated by the l-Asp modification of chitosan film and increased with the increase of the concentration of l-Asp in the chitosan substrate. It was shown that the chelation of calcium ion with l-Asp provided a nucleation centre and the cluster nuclei was formed by adsorbing further PO4 3−, Ca2+, and then HAP deposited on the original HAP coating in the supersaturated calcification solution (SCS). The developed method allows a kinetic evaluation of the induction of organic film on crystal nucleation and the growth of HAP in vitro. [Copyright &y& Elsevier]

Despite the increasing number of applications of biosensors in many fields, the construction of a steady biosensor remains still challenging. The high selectivity and stability of molecularly imprinted polymers for the template molecule make them ideal alternatives as recognition elements for sensors. In this work, the fabrication and characterization of biosensor based on molecularly imprinted electrosynthesized polymers is reported as the first case of imprinting sorbitol. A relevant molecularly imprinted film is prepared by o-phenylenediamine (o-PD) using the electrochemical method. Quartz crystal microbalance is employed as a sensitive apparatus of biosensor for the determination of sorbitol. An equation is deduced to characterize the interaction between molecularly imprinted films and the template. A linear relationship between the frequency shift and the concentration of analyte in the range of 1–15 mM was found. The detection limit is about 1 mM. [Copyright &y& Elsevier]