Electrochemical Detection of Peanut Allergen Ara h 1 Using a Sensitive DNA Biosensor Based on Stem–Loop Probe

A novel electrochemical DNA sensor was developed by using a stem–loop probe for peanut allergen Ara h 1 detection. The probe was modified with a thiol at its 5′ end and a biotin at its 3′ end. The biotin-tagged “molecular beacon”-like probe was attached to the surface of a gold electrode to form a stem–loop structure by self-assembly through facile gold–thiol affinity. 6-Mercaptohexanol (MCH) was used to cover the remnant bare region. The stem–-loop probe was “closed” when the target was absent, and then the hybridization of the target induced the conformational change to “open”, along with the biotin at its 3′ end moved away from the electrode surface. The probe conformational change process was verified by circular dichroism (CD); meanwhile, electron-transfer efficiency changes between probe and electrode were proved by electrochemical impedance spectroscopy (EIS). The detection limit of this method was 0.35 fM with the linear response ranging from 10^–15 to 10^–10 M. Moreover, a complementary target could be discriminated from one-base mismatch and noncomplementarity. The proposed strategy has been successfully applied to detect Ara h 1 in the peanut DNA extracts of peanut milk beverage, and the concentration of it was 3.2 × 10^–13 mol/L

Visible-Light-Stimulated Enzymelike Activity of Graphene Oxide and Its Application for Facile Glucose Sensing

A novel and interesting enzyme-mimicking activity of chitosan-functionalized graphene oxide (CS-GO) upon phototriggering was demonstrated. CS-GO could catalyze oxidation of a typical chromogenic substrate (3,3′,5,5′-tetramethylbenzidine, TMB) under visible light (λ ≥ 400 nm) stimulation, which was independent of destructive H₂O₂. Visible light triggering was a rapid, clean, and versatile means for inducing the enzymelike activity of CS-GO, which was superior to the current peroxidase or peroxidase mimetics that use H₂O₂ as an oxidant. Compared to the natural enzyme horseradish peroxidase (HRP), CS-GO had a higher affinity for TMB. The mechanism of the phototriggered enzyme-mimicking activity of CS-GO was investigated in detail. In addition, a novel and facile colorimetric method was realized for detection of glucose based on the photoactivated CS-GO enzyme-mimicking system and the competitive interaction of concanavalin A with chitosan or glucose. The methodology showed a linear response for glucose in the range 2.5–5.0 mmol/L with a detection limit as low as 0.5 μmol/L. The sensing system was applied for detection of glucose in human serum with satisfactory results

Development and Application of 3‑Chloro-1,2-propandiol Electrochemical Sensor Based on a Polyaminothiophenol Modified Molecularly Imprinted Film

In this work, a novel electrochemical sensor for 3-chloro-1,2-propandiol (3-MCPD) detection based on a gold nanoparticle-modified glassy carbon electrode (AuNP/GCE) coated with a molecular imprinted polymer (MIP) film was constructed. <i>p</i>-Aminothiophenol (<i>p</i>-ATP) and 3-MCPD were self-assembled on a AuNP/GCE surface, and then a MIP film was formed by electropolymerization. The 3-MCPD template combined with <i>p</i>-ATP during self-assembly and electropolymerization, and the cavities matching 3-MCPD remained after the removal of the template. The MIP sensor was characterized by cyclic voltammetry (CV), differential pulse voltammetry (DPV) and scanning electron microscopy (SEM). Many factors that affected the performance of the MIP membrane were discussed and optimized. Under optimal conditions, the DPV current was linear with the log of the 3-MCPD concentration in the range from 1.0 × 10^–17 to 1.0 × 10^–13 mol L^–1 (<i>R</i>² = 0.9939), and the detection limit was 3.8 × 10^–18 mol L^–1 (S/<i>N</i> = 3). The average recovery rate of 3-MCPD from spiked soy sauce samples ranged from 95.0% to 106.4% (RSD < 3.49%). Practically, the sensor showed high sensitivity, good selectivity, excellent reproducibility, and stability during the quantitative determination of 3-MCPD

Ultrasensitive “FRET-SEF” Probe for Sensing and Imaging MicroRNAs in Living Cells Based on Gold Nanoconjugates

MicroRNAs (miRNAs), a kind of single-stranded small RNA molecule, play significant roles in the physiological and pathological processes of human beings. Currently, miRNAs have been demonstrated as important biomarkers critically related to many diseases and life nature, including several cancers and cell senescence. It is valuable to establish sensitive assays for monitoring the levels of intracellular up-regulated/down-regulated miRNA expression, which would contribute to the early prediction of the tumor risk and cardiovascular disease. Here, an oriented gold nanocross (AuNC)-decorated gold nanorod (AuNR) probe with “OFF-enhanced ON” fluorescence switching was developed based on fluorescence resonance energy transfer and surface enhanced fluorescence (FRET-SEF) principle. The nanoprobe was used to specifically detect miRNA in vitro, which gave two linear responses represented by the equation <i>F</i> = 1830.32 log <i>C</i> + 6349.27, <i>R</i>² = 0.9901, and <i>F</i> = 244.41 log <i>C</i> + 1916.10, <i>R</i>² = 0.9984, respectively, along with a detection limit of 0.5 aM and 0.03 fM, respectively. Furthermore, our nanoprobe was used to dynamically monitor the expression of intracellular up-regulated miRNA-34a from the HepG2 and H9C2 cells stimulated by AFB1 and TGF-β1, and the experimental results showed that the new probe not only could be used to quantitively evaluate miRNA oncogene in vitro, but also enabled tracking and imaging of miRNAs in living cells