A fluorometric aptasensor for bisphenol a based on the inner filter effect of gold nanoparticles on the fluorescence of nitrogen-doped carbon dots.

An aptamer-based fluorometric assay is described for the determination of bisphenol A (BPA). The aptamer against BPA is first attached to the surface of the red AuNPs, and this prevents the AuNPs from salt-induced formation of a blue-colored aggregate. Hence, the blue fluorescence of added nitrogen-doped carbon dots (NCDots) is quenched via an inner filter effect (IFE) caused by the red AuNPs. After addition of BPA, the BPA/aptamer complex is formed, and the AuNPs are no longer stabilized agains aggregation. This weakens the IFE and results in the recovery of the fluorescence of the NCDots which is measured best at excitation/emission wavelengths of 300/420 nm. The recovered fluorescence increases linearly in the 10 to 250 nM and 250 to 900 nM BPA concentration ranges, and the detection limit is 3.3 nM. The method was successfully applied to the determination of BPA in spiked environmental tap water samples. Graphical abstract Schematic presentation of a fluorometric aptamer based assay for bisphenol A (BPA). It is based on the inner filter effect of gold nanoparticles (AuNPs) on the fluorescence of nitrogen-doped carbon dots (NCDots).

Colorimetric adenosine aptasensor based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles.

An aptamer based assay is described for the colorimetric detection of adenosine. The presence of adenosine triggers the deformation of hairpin DNA oligonucleotide (HP1) containing adenosine aptamer and then hybridizes another unlabeled hairpin DNA oligonucleotide (HP2). This leads to the formation of a double strand with a blunt 3' terminal. After exonuclease III (Exo III)-assisted degradation, the guanine-rich strand (GRS) is released from HP2. Hence, the adenosine-HP1 complex is released to the solution where it can hybridize another HP2 and initiate many cycles of the digestion reaction with the assistance of Exo III. This leads to the generation of a large number of GRS strands after multiple cycles. The GRS stabilize the red AuNPs against aggregation in the presence of potassium ions. If, however, GRS forms a G-quadruplex, it loses its ability to protect gold nanoparticles (AuNPs) from salt-induced AuNP aggregation. Therefore, the color of the solution changes from red to blue which can be visually observed. This colorimetric assay has a 0.13 nM detection limit and a wide linear range that extends from 5 nM to 1 µM. Graphical abstract Schematic presentation of a colorimetric aptamer biosensor for adenosine detection based on DNA cycling amplification and salt-induced aggregation of gold nanoparticles.

Design of Double Conductive Layer and Grid-Assistant Face-to-Face Structure for Wide Linear Range, High Sensitivity Flexible Pressure Sensors.

Recently, flexible pressure sensors have drawn great attention because of their potential application in human-machine interfaces, healthcare monitoring, electronic skin, etc. Although many sensors with good performance have been reported, researchers mostly focused on surface morphology regulation, and the effect of the resistance characteristics on the performance of the sensor was still rarely systematically investigated. In this paper, a strategy for modulating electron transport is proposed to adjust the linear range and sensitivity of the sensor. In the modulating process, we constructed a double conductive layer (DCL) and grid-assistant face-to-face structure and obtained the sensor with a wide linear range of 0-700 kPa and a high sensitivity of 57.5 kPa-1, which is one of the best results for piezoresistive sensors. In contrast, the sensor with a single conductive layer (SCL) and simple face-to-face structure exhibited a moderate linear range (7 kPa) and sensitivity (2.8 kPa-1). Benefiting from the great performance, the modulated sensor allows for clear pulse wave detection and good recognition of gait signals, which indicates the great application potential in human daily life.

High-performance self-powered integrated system of pressure sensor and supercapacitor based on Cu@Cu2O/graphitic carbon layered porous structure.

With the rapid development of human-machine technology, self-powered pressure sensor integrated systems have been extensively studied. However, there are only a few reports on such multifunctional devices using a single active material. In this work, we report a flexible integrated system, which consists of flexible pressure sensors and supercapacitors. Both of the devices were fabricated based on layered porous Cu@Cu2O/graphitic carbon (Cu@Cu2O/GC) composites, which were obtained by a one-step simple polymer heat treatment method. Due to the discontinuous conductive paths and effective stress concentration relief in the composite, the pressure sensor shows a high sensitivity of 90 kPa-1 in a wide working range of 0-150 kPa, a fast response time of 90 ms, and a detection limit of 2.4 Pa. Moreover, the layered porous structure Cu@Cu2O/GC can not only maintain the integrity of the electrode material, but also promote the diffusion of electrons, enabling super capacitors to obtain excellent electrochemical performance. The specific capacitance of the super capacitor is 17.8 mF cm-2. More importantly, the flexible self-powered integrated system could be directly attached to the human body to detect human motions, showing its great potential application in wearable devices.

Skin-Inspired Hair-Epidermis-Dermis Hierarchical Structures for Electronic Skin Sensors with High Sensitivity over a Wide Linear Range.

The quest for both high sensitivity and a wide linear range in electronic skin design is perpetual; unfortunately, these two key parameters are generally mutually exclusive. Although limited success in attaining both high sensitivity and a wide linear range has been achieved via material-specific or complicated structure design, addressing the conflict between these parameters remains a critical challenge. Here, inspired by the human somatosensory system, we propose hair-epidermis-dermis hierarchical structures based on a reduced graphene oxide/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) aerogel to reconcile this contradiction between high sensitivity and a wide linear range. This hierarchical structure enables an electronic skin (e-skin) sensor linear sensing range up to 30 kPa without sacrificing the high sensitivity (137.7 kPa-1), revealing an effective strategy to overcome the above-mentioned conflict. In addition, the e-skin sensor also exhibits a low detection limit (1.1 Pa), fast responsiveness (∼80 ms), and excellent stability and reproducibility (over 10 000 cycles); as a result, the e-skin platform is capable of detecting small air flow and monitoring human pulse and even sound-induced vibrations. This structure may boost the ongoing research on the structural design and performance regulation of emerging flexible electronics.

[Determination of amanitins and phallotoxins in wild mushrooms by online liquid chromatography-diode array detector-tandem mass spectrometry].

A fast and wide linear range method was established for the determination of mushroom toxins amanitins (α-amanitin,ß-amanitin and γ-amanitin) and phallotoxins (phallacidin and phalloidin) in wild mushrooms by online liquid chromatography-diode array detector-tandem mass spectrometry (LC-DAD-MS/MS). The mushroom toxins were extracted with methanol, and diluted with water. The extracts were separated on an XBridgeTM BEH C18 column (150 mm×3.0 mm, 2.5 µm) under pH 10.7, measured by DAD and then analyzed by MS/MS. Basic mobile phase conditions were applied to improve the ionization efficiency of hydrogen ion adducts. The baseline separation of the analytes was obtained within 15 min. The limits of detection (LODs) of the sample matrix were 0.005-0.02 mg/kg. The toxins were quantified by the results measured by MS/MS when the toxin contents less than 2 mg/kg, and quantified by the results obtained from DAD when the contents more than 2 mg/kg. The linear range was 0.05-500 mg/kg for the whole method in one injection. The method was successfully applied to the analyses of amanitins and phallotoxins in Lepiota brunneoincarnata and white Amanita.