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Dry film resist SU-8 was used to make a thick mold for soft lithography of a poly(dimethylsiloxane) (PDMS) microfluidic chip with deep channels. The stacking of the SU-8 film enabled an ultra-thick (up to 500 μm) resist process on Si wafer. This process was fast and highly reproducible compared with the conventional liquid SU-8 process. The deep channel in the PDMS chip was utilized as a micro-flow cell for sensitive absorbance measurement. Sunset Yellow FCF dye was used to demonstrate absorption spectroscopy in the deep channel. Since the channel depth was proportional to the optical path length, which was proportional to the absorbance value, the PDMS chip achieved a detection limit (15.9 μM) comparable to U- or Z-shaped microfabricated absorbance detection cells in glass. Calibration curves for different solution concentrations were obtained with good R 2 values (～1).

Herein we constructed a deep-red emission fluorescent probe HY for the monitoring of viscosity variation. The probe HY exhibited high selectivity and sensitivity. In 90% glycerol solution, the fluorescence intensity of HY increased significantly compared with pure methanol solution. More importantly, the probe HY has been successfully applied for visualizing viscosity variations in cells and living mice.

In this work, a highly sensitive aptasensor for digoxin determination in biological samples has been introduced. The surface of a gold screen-printed electrode was modified by using electrodeposited gold nanoparticles (GNPs). A monolayer of 3-mercaptopropionic acid (MPA) was then self-assembled on the GNP surfaces. Subsequently, an amino-labeled digoxin specific aptamer was covalently bonded to the carboxylic groups of MPA on the GNPs through imide bond formation. The silver nanoparticle decorated graphene oxide (AgNPs–GO) interacted with the immobilized aptamer via π–π interaction and the oxidation signal of AgNPs was monitored. In the presence of digoxin, the hybrid left the electrode surface due to the specific interaction between the aptamer and digoxin, and the oxidation signal decreased. The proposed aptasensor delivered a linear dynamic range of 1 pM to 0.1 μM and a detection limit of 0.3 pM and was successfully utilized for digoxin determination in biological samples with good reliability.

A direct competitive nanozyme-linked immunosorbent assay (dcNLISA) based on MnO 2 nanosheets (MnO 2 NSs) as a nanozyme label was developed for the highly sensitive determination of fumonisin B 1 (FB 1 ). MnO 2 NS-labeled fumonisin B 1 -bovine serum albumin was easily synthesized as a competing antigen for the dcNLISA. And color changes derived from the MnO 2 –3,3′,5,5′-tetramethylbenzidine (TMB) system were exploited as the output signals of the dcNLISA. Several experimental parameters including the concentrations of the coating antibody, pH values, ionic strength and methanol concentration were optimized. Under the optimal conditions, the proposed method demonstrated a linear range (1.17–20.74 ng mL ?1 ) with a reliable correlation coefficient ( R 2 = 0.9989), a satisfactory limit of detection (0.63 ng mL ?1 ) and high selectivity for the detection of FB 1 . The recoveries of FB 1 in spiked corn and wheat samples were in the range of 85.31–108.16% with coefficients of variation (CVs) ranging from 6.14% to 9.23%. Meanwhile, the testing results showed good consistency ( R 2 = 0.9892) between the developed dcNLISA and the reference method, liquid chromatography/mass spectrometry/mass spectrometry (LC-MS/MS) method. The proposed method was proven to be simple, sensitive, cost-effective and reliable for the screening of FB 1 in cereals.

In this work a facile, sensitive and reliable method was developed and validated for simultaneous analysis of phytosterols, erythrodiol, uvaol, tocopherols and lutein in olive oils. Analytes extracted from saponified olive oils were directly determined by liquid chromatography-mass spectrometry (LC-MS) with atmospheric pressure chemical ionization (APCI). L -Ascorbic acid sodium salt was added into oils as an antioxidant prior to the saponification process, since tocopherols are sensitive to the effect of light and elevated temperature. We found that using L -ascorbic acid sodium salt made the sample treatment become a facile procedure. In this case we no longer need to use amber glass tubes or enwrap the tubes with aluminum foil. Separation was achieved on a C18 column with a gradient of acetonitrile/water (0.1% formic acid). Erythrodiol and uvaol were quantified separately for the first time in HPLC based analysis. The selected ion monitoring (SIM) mass spectra of 14 analytes were measured by using a mass spectrometer with an APCI ion source. Parameters including the linearity of the standard curves, the detection and quantification limits, recovery, repeatability and reproducibility were evaluated for the validation of the method.

Sample preparation, including bacterial lysis, remains a hurdle in the realization of complete point-of-care tests for many pathogens. Here, we developed a sample preparation methodology for enzymatic lysis and sample heating for low-resource, point-of-care applications. We show an instrument-free chemical heater system for rapid lysis of a Gram-positive bacterium ( Staphylococcus aureus ) and an RNA virus (human respiratory syncytial virus) using a dried lysis enzyme mixture (achromopeptidase) for S. aureus . After a lysis step ( 1 minute), lysis enzymes are heat deactivated ( 5 minutes) using a simple disposable chemical heater. We demonstrated that both DNA and RNA in the heat-treated sample could be directly amplified without purification, even in the presence of a clinically-obtained human nasal sample. This simple approach to dry enzyme storage and sample heating is adaptable to many applications where samples need to be lysed, including use in low-resource laboratories and in single-use or cartridge-based point-of-care diagnostic devices.

In the present study, a facile fluorescence turn-on approach for the detection of alkaline phosphatase (ALP) activity has been developed. L -ascorbic acid-2-phosphate (AAP), a substrate of ALP, could be hydrolyzed by ALP to give L -ascorbic acid. L -ascorbic acid then reduced resazurin to resorufin, which resulted in a turn-on fluorescence signal. The fluorescence intensity increase could be directly related to the amount of ALP added to the assay solution. The assay is very sensitive, as 0.12 mU mL ?1 ALP could be clearly detected. Sodium orthovanadate (Na 3 VO 4 ), a well-known ALP inhibitor, was tested, and a clear inhibition effect was observed. The results suggest that our method could be used for ALP activity sensing related various biochemical applications and for the screening of ALP inhibitors.

A ratiometric electrochemical sensor was constructed for sensitive 4-acetamidophenol (4-AP) detection. Ferrocene (Fc) was attached onto a self-assembly of graphene oxide (GO) to form a GO–Fc complex with electrostatic interactions. Furthermore, Nafion was added into the complex in a certain ratio to immobilize the complex. The GO–Fc–Nafion complex was drop-coated on the surface of a glassy carbon electrode (GCE) to prepare a GO–Fc–Nafion/GCE sensing platform. There was a strong, plotted linear relationship between I 4-AP / I Fc and 4-AP concentration in the range from 1 to 100 μM, with a low detection limit of 0.2 μM. This fabricated ratiometric electrochemical sensing platform exhibited high sensitivity and stability responses towards 4-AP, over potential interfering species. Experimental results confirmed high detection stability and recoveries, indicating its high feasibility for 4-AP detection in biological samples.

Magnetic bead-based biosensors are becoming a hot spot in biomedical fields. A Dynabeads-labeled immunoassay has been developed using a micro fluxgate biosensor for the detection of alpha fetoprotein (AFP) and carcinoembryonic antigen (CEA). The micro fluxgate sensors with a rectangular permalloy core with sides of equal width and three-dimensional solenoid coils are fabricated by micro-electro-mechanical-system (MEMS) technology, including thick photoresist lithography and electroplating. The immune reaction of biomarkers is accomplished on a separated Au film substrate surface with a self-assembled layer. Sandwich immunoassay is used to specifically capture and label the biomarker. Dynabeads are conjugated into the biomarker by a streptavidin–biotin system. The micro fluxgate-based sensing system was characterized firstly in different concentrations of Dynabeads. It is found that a concentration as low as 0.1 μg ml ?1 (90 Dynabeads) can be detected by this sensing system with an external magnetic field in the range of 643 μT to 1180 μT. The AFP and CEA with different concentrations were detected by the sensing system. The results reveal that a minimum detectable concentration of 1 pg ml ?1 was achieved in the measuring ranges of 724 μT to 1150 μT for AFP, and 670 μT to 1110 μT for CEA. Compared with a micro fluxgate sensor with a ribbon core for the detection of biomarkers, the micro fluxgate sensor with an electroplated permalloy core possesses a wider linear measuring range, and could make it possible to integrate a micro fluxgate-based biosensing system produced on a large scale, with an expanded application field and reduced costs.

We describe for the first time the fabrication of a paper-based microchip electrophoresis (pME) device with integrated hand-drawn pencil electrodes to perform capacitively coupled contactless conductivity detection (C 4 D). This low-cost device (less than $0.10) revealed great capability to dissipate heat, good injection-to-injection repeatability, and ease of attaching pencil-drawn electrodes on the separation channel. The feasibility of the proposed pME-C 4 D device was successfully demonstrated with the separation of bovine serum albumin and creatinine within 150 s with baseline resolution. The limits of detection values for albumin and creatinine were 20 and 35 μmol L ?1 , respectively. These biomolecules present clinical relevance as evidence of kidney failure. The proposed pME-C 4 D offers great potential to be explored in the diagnosis of diabetes mellitus and heart disease.