Multilayer Ti3 C2 -CNTs-Au Loaded with Cyclodextrin-MOF for Enhanced Selective Detection of Rutin.

In this work, multi-layer Ti3 C2 - carbon nanotubes - gold nanoparticles (Ti3 C2 -CNTs-Au) and cyclodextrin metal-organic framework - carbon nanotubes (CD-MOF-CNTs) have been prepared by in situ growth method and used to construct the ultra-sensitive rutin electrochemical sensor for the first time. Among them, the large number of metal active sites of Ti3 C2 , the high electron transfer efficiency of CNTS, and the good catalytic properties of AuNPs significantly enhance the electrochemical properties of the composite carbon nanomaterials. Interestingly, CD-MOF has a unique host-guest recognition and a large number of cavities, molecular gaps, and surface reactive groups, which gives the composite outstanding accumulation properties and selectivity for rutin. Under the optimized conditions, the constructed novel sensor has satisfactory detection performance for rutin in the range of 2 × 10-9 to 8 × 10-7  M with a limit of detection of 6.5 × 10-10  M. In addition, the sensor exhibits amazing anti-interference performance against rutin in some flavonoid compounds and can be used to test natural plant samples (buckwheat, Cymbopogon distans, and flos sophorae immaturus). This work has promising applications in the field of environmental and food analysis, and exploring new directions for the application of Mxene-based composites.

An ultrasensitive high-performance baicalin sensor based on C3N4-SWCNTs/reduced graphene oxide/cyclodextrin metal-organic framework nanocomposite.

Baicalin (Bn) obtained from natural plants has been found to exhibit significant antiviral activity against Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2). Herein, a novel ultrasensitive Bn electrochemical sensor was proposed based on graphitized carbon-nitride - single-walled carbon nanotube nanocomposites (C3N4-SWCNTs), reduced graphene oxide (rGO) and electrodeposited cyclodextrin-metal organic framework (CD-MOF). The sensing nanomaterials were characterized by X-ray diffraction spectroscopy, X-ray photoelectron spectroscopy, Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. Under optimal conditions, the sensor exhibited sensitive detection of Bn in a wide linear range of 1 × 10-9-5 × 10-7 M with an LOD of 4.6 × 10-10 M and a sensitivity of 220 A/M, and it showed satisfactory stability and accuracy for detecting Bn in real samples (human serum and bear bile scutellaria eye drops). In addition, the electrochemical reaction sites and redox mechanism of Bn were revealed through electrochemical behavior and density functional theory. This work provided an insightful solution for detecting Bn, and extensive potential applications could be further expected.

Selective determination of epinephrine using electrochemical sensor based on ordered mesoporous carbon / nickel oxide nanocomposite.

A nanocomposite of ordered mesoporous carbon/nickel oxide (OMC-NiO) was synthesized by hard-templating method. The nanocomposite remained ordered mesostructure and high surface area with the NiO nanocrystals embedded in the wall of the OMC. A sensitive sensor for electrochemical detection of epinephrine (EP) was developed with GCE modified by OMC-NiO nanocomposite. Cyclic voltammogram (CV) and differential pulse voltammetry (DPV) were used as the techniques to explore the electrochemical behavior of EP on OMC-NiO/GCE surface. The result showed that the electrode demonstrated better electrocatalytic performance to EP compared to that seen at OMC/GCE. Under the optimum condition, DPV measurements of the electrode response displayed a linear detection range for 8.0 × 10-7 to 5.0 × 10-5 M with a detection limit of 8.5 × 10-8 M (S/N = 3). It is worth noting that the electrocatalytic redox mechanism of EP on the electrode have studied through experiments and calculations (cyclic voltammetry and molecular electrostatic potential distribution). Moreover, the electrocatalytic behavior for the oxidation of EP and uric acid (UA) on OMC-NiO/GCE surface was investigated. The result showed that the sensor can be used to selectively determinate EP in the presence of an excesses of UA. Finally, the developed sensor was successfully applied to the determination of EP in spiked human blood serum and EP injection with satisfactory results.

Stimuli-enabled switch-like paracetamol electrochemical sensor based on thermosensitive polymer and MWCNTs-GQDs composite nanomaterial.

A temperature-controlled switchable electrochemical sensor was constructed based on a composite film consisting of thermosensitive block polymer poly(styrene-b-(N-isopropylacrylamide)-b-styrene) (PS-PNIPAm-PS), carboxylated multi-walled carbon nanotubes (MWCNTs-COOH) and amino-functionalized graphene quantum dots (N-GQDs). The prepared sensor showed good temperature sensitivity and reversibility in sensing paracetamol. In the low temperature environment, the polymer stretched to bury the electroactive sites of the carbon nanocomposite, and the paracetamol could not pass through the polymer to achieve electronic exchange, representing the "closed" state. Conversely, in the high temperature environment, the polymer shrank to expose the electroactive sites and enlarge background currents, the paracetamol was able to undergo the redox reaction normally and generate the response current, representing the "on" state. In addition, the sensor had a wide detection range (0.1 to 7.0 µM and 7.0 to 103.0 µM) and a low LOD of 66 nM for paracetamol. This switch-like sensor provided a novel idea for the application of thermosensitive polymers.

Electrochemical dopamine sensor based on the use of a thermosensitive polymer and an nanocomposite prepared from multiwalled carbon nanotubes and graphene oxide.

An electrochemical dopamine sensor with a temperature-controlled switch was constructed by using a mixture of thermo-sensitive block copolymers (type tBA-PDEA-tBA), graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs). If the temperature is below 26 °C, the polymer on the glassy carbon electrode (GCE) is stretched, the distance between the MWCNTs is large, and the charge transfer resistance (Rct) of the composite also is large. In the presence of dopamine, the electron transfer at the electrode is strongly retarded and in the "off" state. At above 38 °C, the polymer is shrunk and the Rct is much smaller. The presence of dopamine results in a rapid electron transfer at the GCE, and this is referred to as the "on" state. At temperatures between 26 and 38 °C, the polymer shrinks slightly and has a "spring-like" state. There is a linear relationship between the response current (typically measured at a potential as low as 0.16 V vs. Ag/AgCl) and temperature. The response to dopamine is linear in the 0.06 to 4.2 µM and 4.2 to 18.2 µM concentration range, and the detection limit is 42 nM. Conceivably, this approach provides a novel approach towards the design of electrochemical sensors based on the use of thermo-sensitive polymers. Graphical abstract Schematic presentation of reversible and temperature-controlled electrochemical response of dopamine on the thermo-sensitive block copolymers (tBA-PDEA-tBA) / multi-walled carbon nanotubes (MWCNTs) / graphene oxide (GO) / glassy carbon electrode (GCE).

Temperature-induced amperometric glucose biosensor based on a poly(N-vinylcaprolactam)/graphene oxide composite film.

A temperature-induced sensing film consisting of poly(N-vinylcaprolactam) (PVCL), graphene oxide (GO) and glucose oxidase (GOD) was fabricated and used to modify a glassy carbon electrode (GCE). The PVCL/GO/GOD/GCE composite film was characterized by electrochemical impedance spectroscopy (EIS). The morphological properties of the composite were investigated by scanning electron microscopy (SEM). The direct electron transfer (DET) of GOD was achieved. GOD at PVCL/GO/GOD/GCE exhibited a couple of well-defined redox peaks with a formal potential of -0.432 V (vs. Ag/AgCl). The composite film showed temperature-induced catalytic activity towards glucose. Large peak currents were observed by amperometry at -0.39 V (vs. Ag/AgCl) when the temperature was above the lower critical solution temperature (LCST) of PVCL, and then disappeared when it was below the LCST. The modified electrode displayed an excellent electrocatalytic response to glucose. The detection of glucose with the composite film ranged from 0.1 to 1.7 mmol L-1 above 35 °C. The constructed biosensor also possesses good stability, reproducibility and anti-interference ability.