Bowei Li

A fast and low-cost spray method for prototyping and depositing surface-enhanced Raman scattering arrays on microfluidic paper based device

In this study, a fast, low‐cost, and facile spray method was proposed. This method deposits highly sensitive surface‐enhanced Raman scattering (SERS) silver nanoparticles (AgNPs) on the paper‐microfluidic scheme. The procedures for substrate preparation were studied including different strategies to synthesize AgNPs and the optimization of spray cycles. In addition, the morphologies of the different kinds of paper substrates were characterized by SEM and investigated by their SERS signals. The established method was found to be favorable for obtaining good sensitivity and reproducible results. The RSDs of Raman intensity of randomly analyzing 20 spots on the same paper or different filter papers depositing AgNPs are both below 15%. The SERS enhancement factor is approximately 2 × 107. The whole fabrication is very rapid, robust, and does not require specific instruments. Furthermore, the total cost for 1000 pieces of chip is less than

Portable paper-based device for quantitative colorimetric assays relying on light reflectance principle

20. These advantages demonstrated the potential for growing SERS applications in the area of environmental monitoring, food safety, and bioanalysis in the future.

Brushing, a simple way to fabricate SERS active paper substrates

This paper presents a novel paper‐based analytical device based on the colorimetric paper assays through its light reflectance. The device is portable, low cost (<20 dollars), and lightweight (only 176 g) that is available to assess the cost‐effectiveness and appropriateness of the original health care or on‐site detection information. Based on the light reflectance principle, the signal can be obtained directly, stably and user‐friendly in our device. We demonstrated the utility and broad applicability of this technique with measurements of different biological and pollution target samples (BSA, glucose, Fe, and nitrite). Moreover, the real samples of Fe (II) and nitrite in the local tap water were successfully analyzed, and compared with the standard UV absorption method, the quantitative results showed good performance, reproducibility, and reliability. This device could provide quantitative information very conveniently and show great potential to broad fields of resource‐limited analysis, medical diagnostics, and on‐site environmental detection.

Ultrasensitive colorimetric detection of Cu2+ ion based on catalytic oxidation of L-cysteine.

A simple and facile method has been demonstrated to fabricate low-cost surface enhanced Raman scattering (SERS) active microfluidic paper chips using a painting brush. This strategy solves the problem of mass production of highly reproducible SERS substrates without complicated or bulky micro- or nanofabrication instruments. Rhodamine 6G (R6G) was chosen as a probe molecule to evaluate the performance of the SERS active chip. To further demonstrate the possibility of this methods potential application in environmental monitoring, trace malachite green (MG) was successfully analyzed on this chip. The performance of our chips was desirable. The paper substrates with silver nanoparticles deposited by brush were found to be cost-efficient and highly sensitive (LOD for R6G and MG are 1 nM and 10 nM, respectively), and have good reproducibility (∼15% relative standard deviation).

A Three-Dimensional Origami Paper-Based Device for Potentiometric Biosensing.

As an essential element, copper ion (Cu(2+)) plays important roles in human beings for its participation in diverse metabolic processes as a cofactor and/or a structural component of enzymes. However, excessive uptake of Cu(2+) ion gives rise to the risk of certain diseases. So, it is important to develop simple ways to monitor and detect Cu(2+) ion. In this study, a simple, facile colorimetric sensor for the ultrasensitive determination of Cu(2+) ion was developed based on the following principle: L-cysteine and 1-chloro-2,4-dinitrobenzene (CDNB) could be conjugated to form the yellow product 2,4-dinitrophenylcysteine (DNPC), which was measurable at 355nm; however, upon addition of Cu(2+) ion, the absorbance of DNPC would be decreased owing to the Cu(2+) ion catalytic oxidation of L-cysteine to L-cystine in the presence of O2. Thus, the colorimetric detection of Cu(2+) ion could be achieved. The optimal pH, buffer, temperature and incubation time for the colorimetric sensor were obtained of pH 6.8 in 0.1M HEPES solution, 90 °C and 50 min, respectively. A good linearity within the range of 0.8-10 nM (r = 0.996) was attained, with a high detectability up to 0.5nM. Analyses of Cu(2+) ion in drinking water, lake water, seawater and biological samples were carried out and the method performances were found to agree well with that obtained by ICP-MS. The developed simple colorimetric sensor proved applicable for Cu(2+) ion determination in real samples with high sensitivity and selectivity.

Micropumps actuated negative pressure injection for microchip electrophoresis

Current paper-based potentiometric ion-sensing platforms are planar devices used for clinically relevant ions. These devices, however, have not been designed for the potentiometric biosensing of proteins or small molecule analytes. A three-dimensional origami paper-based device, in which a solid-contact ion-selective electrode is integrated with an all-solid-state reference electrode, is described for the first time. The device is made by impregnation of paper with appropriate bioreceptors and reporting reagents on different zones. By folding and unfolding the paper structures, versatile potentiometric bioassays can be performed. A USB-controlled miniaturized electrochemical detector can be used for simple and in situ measurements. Using butyrylcholinesterase as a model enzyme, the device has been successfully applied to the detection of enzyme activities and organophosphate pesticides involved in the enzymatic system as inhibitors. The proposed 3D origami paper device allows the potentiometric biosensing of proteins and small molecules in a simple, portable, and cost-effective way.

A glutathione S-transferase from Proteus mirabilis involved in heavy metal resistance and its potential application in removal of Hg2+

A simple negative pressure pinched sample injection method was presented. This method combined diaphragm micropumps and a single voltage supply to generate controllable well‐defined sample plug, and led to effective electrophoresis separation. The pinched plug was found to be favorable for obtaining representative and reproducible results that the RSD of the migration time and peak height of sodium fluorescein were 0.5 and 2.1%, respectively (n=25). The established method had been applied in separation of amino acid samples. This method has the advantages of well‐defined plug, free sample bias effect, high reproducibility and convenience of controlling the negative pressure by the integrated pumps on the microchip. In addition, the single high voltage supply and the world‐to‐chip interface simplified the instrumentation, which is of benefit to the minimization and automation. These advantages demonstrate the potential of this method for a wide range of applications.

Quantum Dot-Based Molecularly Imprinted Polymers on Three-Dimensional Origami Paper Microfluidic Chip for Fluorescence Detection of Phycocyanin

Glutathione S-transferases (GSTs) are a family of multifunctional proteins playing important roles in detoxification of harmful physiological and xenobiotic compounds in organisms. In our study, a gene encoding a GST from Proteus mirabilis strain V7, gstPm-4, was cloned and conditionally expressed in Escherichia coli strain BL21(DE3). The purified GstPm-4 protein, with an estimated molecular mass of approximately 23kDa, was able to conjugate 1-chloro-2,4-dinitrobenzene and bind to the GSH-affinity matrix. Real-time reverse transcriptase PCR suggested that mRNA level of gstPm-4 was increased in the presence of CdCl2, CuCl2, HgCl2 and PbCl2, respectively. Correspondingly, overexpression of gstPm-4 in the genetically engineered bacterium Top10/pLacpGst exhibited higher heavy metal resistance compared to the control Top10/pLacP3. Another genetically engineered bacterium Top10/pBATGst, in which the DNA encoding GstPm-4 protein was fused with the DNA encoding Pfa1-based auto surface display system, was built. Top10/pBATGst could constitutively express the chimeric GstPm-4 and anchor it onto the cell surface subsequently. Almost 100% of the Hg(2+) within the range of 0.1-100 nM was adsorbed by Top10/pBATGst, and 80% of the bounded Hg(2+) could be desorbed from bacterial cells when pH was adjusted to 6.0. Thus, Top10/pBATGst can be potentially used for efficient treatment of Hg(2+)-contaminated aquatic environment.

An optical sensor for monitoring of dissolved oxygen based on phase detection

In this work, we developed a novel strategy using fluorescent quantum dots (QDs) combined with molecularly imprinted polymers (MIPs) on three-dimensional (3D) origami paper-based microfluidic devices for specific recognition and sensitive detection of phycocyanin. This method can realize the liquid phase of QDs@MIPs being transferred to the solid-phase paper base and achieve easy portability for the analysis. Under optimal conditions, we successfully demonstrated the proposed paper@QDs@MIPs 3D microfluidic chip for the sensitive and selective detection of phycocyanin protein target in a simple and robust manner. Our results revealed that the method exhibited a dynamic response to phycocyanin in the range of 10-50 mg/L with a limit of detection of 2 mg/L. Importantly, this device could provide quantitative information very conveniently and show great potential to be further extended to the detection of other proteins or biomarkers for environmental and food safety research.

Microfluidic device for integrated restriction digestion reaction and resulting DNA fragment analysis

Dissolved oxygen (DO) monitoring is of vital importance to water treatment, sewage treatment, aquaculture and biological research. The traditional method for DO detection is an electrochemical method called the Clark electrode. This electrochemical method has been widely used as it is simple and inexpensive; however, the critical drawback for this kind of sensor is that it is easily affected by pH variations, and by the concentration of H2S and SO2. Optical sensing for DO detection is a newly developed technology, which can avoid most of the drawbacks of the electrochemical sensors. A DO sensor using fluorescence detection is described in this paper. The oxygen concentration measurement principle is based on optical phase detection, which is more precise than the traditional intensity detection method. Emission is carried out by a low-cost, specially designed light emitting diode (LED) source. To avoid an unwanted phase shift, a reference LED is used to improve the degree of accuracy. The sensing material for fluorescence is a ruthenium complex. A discrete Fourier transform (DFT) algorithm was used for the phase calculation. The system was designed into a stainless steel probe, and dissolved oxygen concentration measurement results for various applications are presented in this paper.