Tanom Lomas

Inkjet-printed graphene-PEDOT:PSS modified screen printed carbon electrode for biochemical sensing

In this work, a novel method for electrode modification based on inkjet-printing of electrochemically synthesized graphene-PEDOT:PSS (GP-PEDOT:PSS) nanocomposite is reported for the first time. GP-PEDOT:PSS dispersed solution is prepared for use as an ink by one-step electrolytic exfoliation from a graphite electrode. GP-PEDOT:PSS layers are then printed on screen printed carbon electrodes (SPCEs) by a commercial inkjet material printer (Dimatrix Inc.) and their electrochemical behaviors towards three common electroactive analytes, including hydrogen peroxide (H2O2), nicotinamide adenine dinucleotide (NAD+/NADH) and ferri/ferro cyanide (Fe(CN)63−/4−) redox couples, are characterized. It is found that the oxidation signals for H2O2, NADH and K2Fe(CN)6 of PEDOT:PSS modified and GP-PEDOT:PSS modified SPCEs are ∼2–4 and ∼3–13 times higher than those of unmodified SPCE, respectively. In addition, excellent analytical features with relatively wide dynamic ranges, high sensitivities and low detection limits have been achieved. Therefore, the inkjet-printed GP-PEDOT:PSS electrode is a promising candidate for advanced electrochemical sensing applications.

Facile preparation of graphene–metal phthalocyanine hybrid material by electrolytic exfoliation

In this article, we present a new, facile and efficient electrochemical method for the production of a stable aqueous dispersion of a graphene–metal phthalocyanine hybrid material. The material has been prepared by electrolytic exfoliation of graphite in an electrolyte containing copper phthalocyanine-3,4′,4′′,4′′′-tetrasulfonic acid tetrasodium salt (TSCuPc). Single- and few-layer graphene sheets, decorated with metal phthalocyanine molecules, are generated during the electrolysis and stably dispersed in the electrolyte with no further chemical treatment. Scanning electron/atomic force microscopic characterization shows that the TSCuPc–graphene hybrid structure has a sharp-edged particle morphology with thicknesses ranging from 2 nm to 6 nm, corresponding to 1 to 6 graphene-stacked layers and largely varied lateral dimensions from a few tens to several hundreds of nanometers. In addition, Raman/FTIR/UV-Vis spectra and X-ray diffraction reveal characteristic peaks that suggest that the TSCuPc–graphene hybrid is formed by non-covalent π–π interactions between graphene sheets and metal phthalocyanine and indicate a high quality graphene hybrid structure that can potentially be used in practical applications.

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.

Design, Fabrication and Analysis of Silicon Hollow Microneedles for Transdermal Drug Delivery System for Treatment of Hemodynamic Dysfunctions

In this paper, we present design, fabrication and coupled multifield analysis of hollow out-of-plane silicon microneedles with piezoelectrically actuated microfluidic device for transdermal drug delivery (TDD) system for treatment of cardiovascular or hemodynamic disorders such as hypertension. The mask layout design and fabrication process of silicon microneedles and reservoir involving deep reactive ion etching (DRIE) is first presented. This is followed by actual fabrication of silicon hollow microneedles by a series of combined isotropic and anisotropic etching processes using inductively coupled plasma (ICP) etching technology. Then coupled multifield analysis of a MEMS based piezoelectrically actuated device with integrated silicon microneedles is presented. The coupledfield analysis of hollow silicon microneedle array integrated with piezoelectric micropump has involved structural and fluid field couplings in a sequential structural-fluid analysis on a three-dimensional model of the microfluidic device. The effect of voltage and frequency on silicon membrane deflection and flow rate through the microneedle is investigated in the coupled field analysis using multiple code coupling method. The results of the present study provide valuable benchmark and prediction data to fabricate optimized designs of the silicon hollow microneedle based microfluidic devices for transdermal drug delivery applications.

Wireless black box using MEMS accelerometer and GPS tracking for accidental monitoring of vehicles

In this work, wireless black box using MEMS accelerometer and GPS tracking system is developed for accidental monitoring. The system consists of cooperative components of an accelerometer, microcontroller unit, GPS device and GSM module. In the event of accident, this wireless device will send mobile phone short massage indicating the position of vehicle by GPS system to family member, emergency medical service (EMS) and nearest hospital. The threshold algorithm and speed of motorcycle are used to determine fall or accident in real-time. The system is compact and easy to install under rider seat. The system has been tested in real world applications using bicycles. The test results show that it can detect linear fall, non-linear fall and normal ride with high accuracy.

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).

AAO-CNTs electrode on microfluidic flow injection system for rapid iodide sensing

In this work, carbon nanotubes (CNTs) nanoarrays in anodized aluminum oxide (AAO-CNTs) nanopore is integrated on a microfluidic flow injection system for in-channel electrochemical detection of iodide. The device was fabricated from PDMS (polydimethylsiloxane) microchannel bonded on glass substrates that contains three-electrode electrochemical system, including AAO-CNTs as a working electrode, silver as a reference electrode and platinum as an auxiliary electrode. Aluminum, stainless steel catalyst, silver and platinum layers were sputtered on the glass substrate through shadow masks. Aluminum layer was then anodized by two-step anodization process to form nanopore template. CNTs were then grown in AAO template by thermal chemical vapor deposition. The amperometric detection of iodide was performed in 500-μm-wide and 100-μm-deep microchannels on the microfluidic chip. The influences of flow rate, injection volume and detection potential on the current response were optimized. From experimental results, AAO-CNTs electrode on chip offers higher sensitivity and wider dynamic range than CNTs electrode with no AAO template.

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.

Humidity sensor based on piezoresistive microcantilever with inkjet printed PEDOT/PSS sensing layers

In this work, a new humidity sensor is developed by employing piezoresistive microcantilever with inkjet printed PEDOT/PSS sensing layers. 200 µm long, 50 µm wide and 3.75 µm thick microcantilever is designed and fabricated by PolyMUMP, which is a commercial Multi-User MEMS Process. The polysilicon piezoresistive layer in the microcantilever acts as a transduction component that will change its resistance when there is bending of microcantilever due adsorbed water molecules on PEDOT/PSS sensing layers. PEDOT/PSS layers are directly patterned on microcantilever by a commercial Dimatrix material inkjet printer. The resistances of microcantilever sensors are monitored as a function of humidity, which is simultaneously measured by a commercial humidity sensor. The resistance value is found to decrease with the humidity and the calibration curve of resistance change is linearly proportional to the percent of relative humidity in range from 20.3–66.3 %RH with high sensitivity. The results show that the piezoresistive microcantilever sensor with inkjet printed PEDOT/PSS sensing layers is a promising candidate for humidity sensing.