Effects of Physicochemical Parameters on Struvite Crystallization Based on Kinetics.

The precipitation of struvite (MgNH4PO4·6H2O) is considered to be a promising method for the recovery of phosphate from wastewater. In this review, the kinetic models, which are commonly used to explain the process of struvite crystallization, are described. The mixed-suspension mixed-product removal (MSMPR) model is based on the population balance equation (the size-dependent growth model and the size-independent growth model). Thereafter, the first-order kinetic fitting model that aligned with concentration changes in the substrate is summarized. Finally, the several physical and chemical factors that affected the efficiency of struvite crystallization are determined. The supersaturation ratio, which is seen as the driving force of struvite crystallization, is the main factor that influences crystallization; however, it cannot be used in practical applications of engineering because it is indirectly associated with the following factors: pH, the molar ratio of Mg:N:P, and the interference of foreign impurities. In this study, we present conclusions that should be used to guide further research studies, and encourage the engineering practice of wastewater treatment with struvite precipitation.

A high-precision thermometry microfluidic chip for real-time monitoring of the physiological process of live tumour cells.

Temperature changes in cells are generally accompanied by physiological processes. Cellular temperature measurements can provide important information to fully understand cellular mechanisms. However, temperature measurements with conventional methods, such as fluorescent polymeric thermometers and thermocouples, have limitations of low sensitivity or cell state disturbance. We developed a microfluidic chip integrating a high-precision platinum (Pt) thermo-sensor that can culture cells and monitor the cellular temperature in situ. During detection, a constant temperature system with a stability of 0.015 °C was applied. The temperature coefficient of resistance of the Pt thermo-sensor was 2090 ppm/°C, giving a temperature resolution of the sensor of less than 0.008 °C. This microchip showed a good linear correlation between the temperature and resistance of the Pt sensor at 20-40 °C (R2 = 0.999). Lung and liver cancer cells on the microchip grew normally and continuously. The maximum temperature fluctuation of H1975 (0.924 °C) was larger than that of HepG2 (0.250 °C). However, the temperature of adherent HepG2 cells changed over time, showing susceptibility to the environment most of the time compared to H1975. Moreover, the temperature increment of non-cancerous cells, such as hepatic stellate cells, was monitored in response to the stimulus of paraformaldehyde, showing the process of cell death. Therefore, this thermometric microchip integrated with cell culture could be a non-disposable and label-free tool for monitoring cellular temperature applied to the study of physiology and pathology.

A batch microfabrication of a microfluidic electrochemical sensor for rapid chemical oxygen demand measurement.

Chemical oxygen demand (COD) is one of the key water quality parameters in environmental monitoring. However, fabricating a COD sensor with the characteristic of batch-processing and rapid measurement is always a challenging issue. This paper reports a microfluidic electrochemical sensor for the organic matter measurement based on advanced oxidization within a fixed microvolume detection chamber by a microfabrication technique/MEMS. By fabricating a silicon-based Ag/AgCl reference electrode and employing PbO2 as the working electrode with Pt as the counter electrode, we verified the superiority of the as-fabricated sensor by continuous potassium acid phthalate detection; an acceptable limit of detection (4.17 mg L-1-200 mg L-1), a low limit of detection (2.05 mg L-1), a desirable linearity (R2 = 0.982) and relative stability at different pH values and Cl- concentrations was witnessed. Particularly, a shorter detection time (2 s) was witnessed for the as-proposed sensor compared with traditional organic matter measurement methods. Each sensing process takes only 2 seconds for sensing because a micro-cavity with a volume of 2.5 µL was fabricated and used as a detection pool. Moreover, as the sensor was fabricated by a mass-production technique, potential response consistency of multiple sensors was expected and was verified via a series of parallel experiments. In this paper, a miniaturized (8 mm × 10 mm), low-cost and reliable COD sensor was designed and fabricated by MEMS, and it provided a core sensor component for construction of an online water environment monitoring network to meet the substantial demand for COD sensors in the Internet of Things (IOT) era.

Graphene oxide functionalized long period grating for ultrasensitive label-free immunosensing.

We explore graphene oxide (GO) nanosheets functionalized dual-peak long period grating (dLPG) based biosensor for ultrasensitive label-free antibody-antigen immunosensing. The GO linking layer provides a remarkable analytical platform for bioaffinity binding interface due to its favorable combination of exceptionally high surface-to-volume ratio and excellent optical and biochemical properties. A new GO deposition technique based on chemical-bonding in conjunction with physical-adsorption was proposed to offer the advantages of a strong bonding between GO and fiber device surface and a homogeneous GO overlay with desirable stability, repeatability and durability. The surface morphology of GO overlay was characterized by Atomic force microscopy, Scanning electron microscope, and Raman spectroscopy. By depositing the GO with a thickness of 49.2nm, the sensitivity in refractive index (RI) of dLPG was increased to 2538nm/RIU, 200% that of non-coated dLPG, in low RI region (1.333-1.347) where bioassays and biological events were usually carried out. The IgG was covalently immobilized on GO-dLPG via EDC/NHS heterobifunctional cross-linking chemistry leaving the binding sites free for target analyte recognition. The performance of immunosensing was evaluated by monitoring the kinetic bioaffinity binding between IgG and specific anti-IgG in real-time. The GO-dLPG based biosensor demonstrates an ultrahigh sensitivity with limit of detection of 7ng/mL, which is 10-fold better than non-coated dLPG biosensor and 100-fold greater than LPG-based immunosensor. Moreover, the reusability of GO-dLPG biosensor has been facilitated by a simple regeneration procedure based on stripping off bound anti-IgG treatment. The proposed ultrasensitive biosensor can be further adapted as biophotonic platform opening up the potential for food safety, environmental monitoring, clinical diagnostics and medical applications.

Immobilization of biomolecules on cysteamine-modified polyaniline film for highly sensitive biosensing.

We present a new cysteamine (CS)-modified polyaniline (PANI) film for highly efficient immobilization of biomolecules in biosensing technology. This electrochemical deposited PANI film treated with CS and glutaraldehyde could be employed as an excellent substrate for biomolecules immobilization. The parameters of PANI growth were optimized to obtain suitable surface morphology of films for biomolecules combination with the help of electron and atomic force microscopy. Cyclic voltammetry (CV) was utilized to illustrate the different electrochemical activities of each modified electrode. Due to the existence of sulfydryl group and amino group in CS, surface modification with CS was proven to reduce oxidized units on PANI film remarkably, as evidenced by both ATR-FTIR and Raman spectroscopy characterizations. Furthermore, bovine serum albumin (BSA) was used as the model protein to investigate the immobilization efficiency of biomolecules on the PANI film, comparative study using quartz crystal microbalance (QCM) showed that BSA immobilized on CS-modified PANI could be increased by at least 20% than that without CS-modified PANI in BSA solution with the concentration of 0.1-1mg/mL. The CS-modified PANI film would be significant for the immobilization and detection of biomolecules and especially promising in the application of immunosensor for ultrasensitive detection.

A hydrophilic polymer based microfluidic system with planar patch clamp electrode array for electrophysiological measurement from cells.

This paper presents a microfluidic planar patch clamp system based on a hydrophilic polymer poly(ethylene glycol) diacrylate (PEGDA) for whole cell current recording. The whole chip is fabricated by UV-assisted molding method for both microfluidic channel structure and planar electrode partition. This hydrophilic patch clamp chip has demonstrated a relatively high gigaseal success rate of 44% without surface modification compared with PDMS based patch clamp devices. This chip also shows a capability of rapid intracellular and extracellular solution exchange with high stability of gigaseals. The capillary flow kinetic experiments demonstrate that the flow rates of PEGDA microfluidic channels are around two orders of magnitude greater than those for PDMS-glass channels with the same channel dimensions. This hydrophilic polymer based patch clamp chips have significant advantages over current PDMS elastomer based systems such as no need for surface modification, much higher success rate of cell gigaseals and rapid solution exchange with stable cell gigaseals. Our results indicate the potential of these devices to serve as useful tools for pharmaceutical screening and biosensing tasks.

Integrated biochip for label-free and real-time detection of DNA amplification by contactless impedance measurements based on interdigitated electrodes.

Here, we introduce an integrated biochip which offers accurate thermal control and sensitive electrochemical detection of DNA amplification in real-time. The biochip includes a 10-µl microchamber, a temperature sensor, a heater, and a contactless impedance biosensor. A pair of interdigitated electrodes is employed as the impedance biosensor and the products of the amplification are determined directly through tracing the impedance change, without using any labels, redox indicators, or probes. Real-time monitoring of strand-displacement amplification and rolling circle amplification was successfully performed on the biochip and a detection limit of 1 nM was achieved. Amplification starting at an initial concentration of 10 nM could be discriminated from that starting at 1 nM started concentration as well as from the negative control. Since an insulation layer covers the electrodes, the electrodes are spared from erosion, hydrolysis and bubble formation on the surface, thus, ensuring a long lifetime and a high reusability of the sensor. In comparison to bench-top apparatus, our chip shows good efficiency, sensitivity, accuracy, and versatility. Our system requires only simple equipments and simple skills, and can easily be miniaturized into a micro-scale system. The system will then be suitable for a handheld portable device, which can be applied in remote areas. It covers merits such as low cost, low-power consumption, rapid response, real-time monitoring, label-free detection, and high-throughput detection.

Covalently immobilized biomolecule gradient on hydrogel surface using a gradient generating microfluidic device for a quantitative mesenchymal stem cell study.

Precisely controlling the spatial distribution of biomolecules on biomaterial surface is important for directing cellular activities in the controlled cell microenvironment. This paper describes a polydimethylsiloxane (PDMS) gradient-generating microfluidic device to immobilize the gradient of cellular adhesive Arg-Gly-Asp (RGD) peptide on poly (ethylene glycol) (PEG) hydrogel. Hydrogels are formed by exposing the mixture of PEG diacrylate (PEGDA), acryloyl-PEG-RGD, and photo-initiator with ultraviolet light. The microfluidic chip was simulated by a fluid dynamic model for the biomolecule diffusion process and gradient generation. PEG hydrogel covalently immobilized with RGD peptide gradient was fabricated in this microfluidic device by photo-polymerization. Bone marrow derived rat mesenchymal stem cells (MSCs) were then cultured on the surface of RGD gradient PEG hydrogel. Cell adhesion of rat MSCs on PEG hydrogel with various RGD gradients were then qualitatively and quantitatively analyzed by immunostaining method. MSCs cultured on PEG hydrogel surface with RGD gradient showed a grated fashion for cell adhesion and spreading that was proportional to RGD concentration. It was also found that 0.107-0.143 mM was the critical RGD concentration range for MSCs maximum adhesion on PEG hydrogel.

Application of poly(dimethylsiloxane)/glass microchip for fast electrophoretic separation of serum small, dense low-density lipoprotein.

Due to the mounting evidence of altered low-density lipoprotein (LDL) size in several disease states, there has been an increasing interest in developing new analytical methods for small, dense low-density lipoprotein (sdLDL) for diagnosis. The present report demonstrates that sdLDL analysis can be performed in a poly(dimethylsiloxane) (PDMS/glass) microchannel. n-Dodecyl beta-D-maltoside (DDM) was utilized to alter channel surface to make it become hydrophilic and nonionic, thus reducing the interaction between the protein and the surface. Moreover, hydroxypropylcellulose (HPC) was added into the running buffer to suppress the adsorption of analytes and also to serve as a sieving matrix. Under optimal conditions, two baseline separations of lipoproteins including high-density lipoprotein (HDL), sdLDL, and lLDL were achieved with different selectivity. LDL particles shown on the electropherogram were also identified by several procedures. This method affords high separation speed and high reproducibility. The intraassay and interassay RSDs of lipoprotein migration times were in the range of 2.01-2.45%. The variation of serum sdLDL of a patient between prior treatment and post-treatment was assessed by this method. This system has the potential for rapid and sensitive detection of different LDL forms, and thus will be applicable to clinical diagnosis.

[Rapid detection of the genotyping of hepatitis C virus using DNA chip with coloration methods].

OBJECTIVE: To develop a new DNA chip with coloration, which can be used for rapid and economical detection of the genotyping of hepatitis C virus (HCV). METHODS: Probes and primers were designed according to the sequence of HCV 5' non-coding region (5' NCR) to fabricate DNA chip. Experimental group consisted of 60 positive serum samples and control group consisted of 20 negative serum samples. To obtain the aimed gene, then they were hybridized with DNA chip. Finally, the results showed in a nylon film. The results of DNA sequencing of samples were used as the control in double blind experimental. RESULTS: Using DNA chip, HCV was detected in positive of all serum specimens of experimental group and negative in control group. The determination of HCV genotype by DNA chip showed corresponding rate of 96.7% with those by sequence assay. CONCLUSION: It showed higher specialty and sensitivity using DNA chip to detect the genotype of HCV. It would be valuable for the clinical genotyping of HCV