Thitima Maturos

Flow injection based microfluidic device with carbon nanotube electrode for rapid salbutamol detection

A microfabicated flow injection device has been developed for in-channel electrochemical detection (ECD) of a beta-agonist, namely salbutamol. The microfluidic system consists of PDMS (polydimethylsiloxane) microchannel and electrochemical electrodes formed on glass substrate. The carbon nanotube (CNT) on gold layer as working electrode, silver as reference electrode and platinum as auxiliary electrode were deposited on a glass substrate. Silver, platinum, gold and stainless steel catalyst layers were coated by DC-sputtering. CNTs were then grown on the glass substance by thermal chemical vapor deposition (CVD) with gravity effect and water-assisted etching. 100-microm-deep and 500-microm-wide PDMS microchannels fabricated by SU-8 molding and casting were then bonded on glass substrate by oxygen plasma treatment. Flow injection and ECD of salbutamol was performed with the amperometric detection mode for in-channel detection of salbutamol. The influences of flow rate, injection volume, and detection potential on the response of current signal were optimized. Analytical characteristics, such as sensitivity, repeatability and dynamic range have been evaluated. Fast and highly sensitive detection of salbutamol have been achieved. Thus, the proposed combination of the efficient CNT electrode and miniaturized lab-on-a-chip is a powerful platform for beta-agonists detection.

Portable microfluidic system for determination of urinary creatinine

A simple, low cost and portable microfluidic system based on a two-point alkaline picrate kinetic reaction has been developed for the determination of urinary creatinine. The creatinine reacts with picric acid under alkaline conditions, forming an orange-red colour, which is monitored on PDMS microchip using a portable miniature fibre optic spectrometer at 510 nm. A linear range was displayed from 0 to 40 mg L(-1) creatinine (r2 = 0.997) with a detection limit of 3.3 mg L(-1) (S/N = 3). On-chip absorbance signals are reproducible, with relative standard deviations (RSDs) of 7.1%, when evaluated with 20 mg L(-1) creatinine (n = 10). The standard curves in which the intra-run CVs (4.7-6.8%) and inter-run CVs (7.9%) obtained were performed on three different days and exhibited good reproducibility. The method was highly correlated with the conventional spectrophotometric method when real urine samples were evaluated (r2 = 0.948; n = 15).

Inkjet printing PEDOT:PSS using desktop inkjet printer

PEDOT:PSS has been used recently into many organic-based devices in order to help charge transfer and improve efficiency of the devices. PEDOT:PSS exhibit various interesting properties. It posses relatively good electrochemical, ambient, and thermal stability of its electrical properties as compared with the other polythiophenes. One aim of manufacturing organic-based device is to lowering the fabrication cost. Due to PEDOT:PSSs stability , it is possible to pattern PEDOT:PSS using inkjet printing. We found that using the CANON IP4500 desktop inkjet printer, the structure of 150 micron could be patterned on PET substrate. By modifying the surface properties of the substrate , the structure of 20 micron could be achieved. The conductivity of inkjet printed PEDOT:PSS could be further enhanced by annealing at 80 C. The conductivity could be 3 times improved. The morphology of the annealed PEDOT:PSS was further investigated using atomic force microscopy(AFM) and the cause for conductivity enhancement could be explained via localization length extension in variable range hopping theory.

On-Chip Immunoassay for Determination of Urinary Albumin

An immunoassay performed on a portable microfluidic device was evaluated for the determination of urinary albumin. An increase in absorbance at 500 nm resulting from immunoagglutination was monitored directly on the poly(dimethylsiloxane) (PDMS) microchip using a portable miniature fibre-optic spectrometer. A calibration curve was linear up to 10 mg L–1 (r2 = 0.993), with a detection limit of 0.81 mg L–1 (S/N = 3). The proposed system showed good precision, with relative standard deviations (RSDs) of 5.1%, when evaluated with 10 mg L–1 albumin (n = 10). Determination of urinary albumin with the proposed system gave results highly similar to those determined by the conventional spectrophotometric method using immunoturbidimetric detection (r2 = 0.995; n = 15).

DNA hybridization enhancement using piezoelectric microagitation through a liquid coupling medium

In conventional DNA microarray hybridization, delivery of target cDNAs to surface-bounded probes depends solely on diffusion, which is notoriously slow, and thus typically requires 6-20 h to complete. In this study, piezoelectric microagitation through a liquid coupling medium is employed to enhance DNA hybridization efficiency and the results are compared with the standard static hybridization method. DNA hybridization was performed in a sealed aluminium chamber containing DNA microarray glass chip, coupling medium and piezoelectric transducers. 3×SSC (Saline Sodium Citrate) was used as a coupling medium to prevent overheating of the piezoelectric transducers and to effectively transmit ultrasonic wave to the glass chip. Flow visualization using fluidic dye and velocimetry (PTV) technique was applied to observe fluid transport in the hybridization chamber. It was revealed that the dye solution was homogeneously distributed within 10 min under dynamic agitation while it took over 1 h to reach the same level of homogeneity in static condition. Plasmodium falciparum DNA microarrays and total RNA extracted from parasite cells were used as a model for DNA microarray experiments. It was found that the required hybridization time may be substantially reduced from 16 h to 4 h by the use of dynamic hybridization scheme. With the same hybridization time of 16 h, dynamic hybridization resulted in higher fluorescent signals of ∼33% and ∼24% compared to static hybridization in Cy3 and Cy5 channels, respectively. Additionally, good/effective spots, some of which were not formed by static method, were enhanced and distributed more uniformly over the microarray. Therefore, the developed dynamic hybridization with integrated piezoelectric microagitation platform is highly promising for DNA analysis in molecular biology and medical applications.

The IoT wearable stretch sensor using 3D-Graphene foam

In this work, we have developed flexible and wearable Stretch Sensor based on the Internet of thing technology. These sensors were realized using a 3D-Graphene foam amalgam with Polydimethylsiloxane (PDMS). To demonstrate the 3D-graphene foam sensors, we constructed an armband muscle measurement using such sensors and developed software based on IoT for real-time muscle expansion and stretch tracking. Wi-Fi was used to transfer data from the sensor to a cloud via web-socket based on Node.js. The data are display expansion of muscle on a website. This muscle stretch tracking is very useful in many contexts such as workout performance measuring, rehabilitation and tele-robotics application. The wearable stretch sensor is consisting of two pieces of 5 centimeters 3D-graphene foam strip and packed with clasped by conductive epoxy. For accuracy, at the end of sensor edge are coated with silver paste for better conductivity. Main CPU uses Intel Edison, which made the sensor connect to the Internet easier. In order to deploy this sensor with another application the ADXL335 was chosen as a 3-axis accelerometer for tracking of gestures or fitness tracking application. An accelerometer was attached to the down side of the Intel Edison main CPU board and including battery and analog to digital converter circuit.

Development of low-cost microfluidic systems for lab-on-a-chip biosensor applications

In this work, we develop low-cost microfluidic systems based on polydimethylsiloxane (PDMS) for lab-on-a-chip applications. PDMS microfluidic structures have been fabricated by micromolding, PDMS casting, and plasma bonding processes. The micromolding technique is used to fabricate PDMS slabs with micro-sized grooves, and the complete microchannel is formed by bonding PDMS slab with glass or PDMS substrate. The molding procedure using SU-8 photoresist patterning on silicon wafer, PDMS microchannel fabrication, and PDMS surface treatment using oxygen plasma and TiO2 coating, are discussed. The various parameters for oxygen plasma treatment including RF power and treatment time are studied in order to obtain conditions for good bonding with the glass substrate. The best condition for plasma treatment is found to be the low RF power (8 W) with 5 min treatment time. In addition, TiO2 coating with oxygen plasma treatment has been applied to make PDMS surface more hydrophilic to improve aqueous solution compatilbility. The microfluidic channels for various applications, including sample injection cross channel, micropump channel, T and Y sample mixers, PCR thermocyling chamber and channel, capillary electrophoresis flow channel, and conductimetric systems have been fabricated. Finally, a typical application of the PDMS chip in a flow injection conductimetric system for sodium chloride detection has been demonstrated.

Low cost hot embossing process for plastics microfluidic chips fabrication

In this work, we develop plastic microfluidic chips based on low cost hot embossing process with metal micromold. Metal micromold was formed on aluminum substrates by CNC milling machine and high precision micromachine. The hot embossing system is in-house made with computer aid design by Solid Work program. The system consists of four main parts, structural body, heating system, compressive system and control electronics. The compressive system consists of two top hydraulic single-stage pistons and four middle-stage pistons. Polymethyl methacrylate (PMMA) microfluidic chips were then produced by hot embossing under different applied temperatures and time. It was found that optimum temperature and time for minimum contraction and depth error were 80 degree C and 2–5 minutes. The developed technique offer advantages for microfluidic chip fabrication in term of quality, complexity and cost.

Development of traveling wave dielectrophoretic (twDEP) microfluidic system

In this work, we present a microfluidic system consisting of 16 parallel electrodes array for cell manipulation by traveling wave dielectophoretic force and electronic circuit design for creating driving signal. Polystyrene microspheres suspensions in water were used as the tested cells. Cells respond to the electric field in various mechanisms depending on the frequency of applied AC signals. When the frequency of applied AC fields is in the range where dielectrophoresis (DEP) is negative, cells experience twDEP force in such a way that they were repelled from the electrode rather than being trapped by positive DEP. The driving signals in the system are created by economical electronic circuit. As the frequency of the applied signals is in the range of 50-700 kHz, cells were move under the influence of twDEP force. As the frequency of the applied signals is more than 700 kHz, cells started moving out of the center between electrodes. These results are consistent with the theory. Because of the fact that twDEP force depends on the effective polarizability and size of particle, it gives us a chance to make the device for cells fraction and separation which can be further applied in biological and medical application such as motion control and cell selectivity.

Single plate electrowetting on dielectric biochip

Electrowetting is well known method for microfluidic technology that plays a critical role in lab-on-a-chip systems by delivering chemical or biological samples. Once electrical potential is applied, the contact angels change and driving the droplet. In this report, a single-plate electrowetting on dielectric (EWOD) was fabricated and tested, containing both the control and ground square-shaped electrodes on one plate with dimension of 2 mm width and 2 mm long, fabricateded by thin film deposition methods and micromolding process. For droplet transportation, we designed electrical circuits using a microcontroller to control relays that switching voltage applied to control electrodes on and off. Interfacing RS232 with microcontroller makes the droplet transporting can be modified from personal computer by sending commands from a PC to a microcontroller.