Development of an immunoFET biosensor for the detection of biotinylated PCR product.

ImmunoFET (IMFET) biosensor is a simple platform for the detection of biotinylated products of polymerase chain reaction (PCR). Construction of the IMFET biosensor started with adsorption of 1.5 mg/mL of protein A (PA) onto the insulated gate surface of ISFET for 90 min. Next, the immobilized 1/500 dilution of anti-biotin antibody was adsorbed onto the PA layer for 60 min. The IMFET biosensor was subsequently ready for detection of the biotinylated amplicon. The IMFET biosensor showed highly specific binding to the biotinylated PCR product of the phaE gene of Haloquadratum walsbyi DSM 16854. The phaE gene is a biomarker of polyhydroxyalkanoate (PHA) producers that contain PHA synthase class III. The lowest amount of DNA template of H. walsbyi DSM 16854 that the IMFET biosensor could detect was 125 fg. The IMFET biosensor has a lower amount of detection compared with a DNA lateral flow biosensor from our previous study. The degree of linearity of the biosensor signal was influenced by the concentration of the biotinylated amplicon. The IMFET biosensor also has a short response time (approximately 30 times) to detect the phaE amplicon compared to an agarose gel electrophoresis. The IMFET biosensor is a promising tool for the detection of the biotinylated PCR product, and it can be integrated into a micro total analysis system (µTAS).

A silicon nitride ISFET based immunosensor for Ag85B detection of tuberculosis.

A silicon nitride Ion Sensitive Field Effect Transistor (ISFET) based immunosensor was developed as a low-cost and label-free electrical detection for the detection of antigen 85 complex B (Ag85B). The sensing membrane of the ISFET was modified with 3-aminopropyltriethoxysilane (APTES) followed by glutaraldehyde (GA), yielding an aldehyde-terminated surface. This group is available for immobilization of a monoclonal antibody against a recombinant Ag85B protein (anti-Ag85B antibody). The optimal concentration for anti-Ag85B antibody immobilization onto the modified ISFET was 100 µg ml-1. This optimal condition provided the maximal binding capability and minimal non-specific background signal. The binding event between the recombinant Ag85B antigen and anti-Ag85B antibody on the ISFET surface is presented by monitoring the gate potential change at a constant drain current. The dose response for the recombinant Ag85B protein showed a linear response between 0.12 and 1 µg ml-1 without significant interference from other recombinant proteins. The analytical imprecision (CV%) and accuracy of this Ag85B protein biosensor were 9.73-10.99% and 95.29%, respectively. In addition, an irrelevant antibody and other recombinant proteins were employed as a negative control to demonstrate the non-specific interaction of the antigen and antibody. The success of this immunosensor system for Ag85B protein detection facilitates the construction of a promising device which can shorten the turnaround time for the diagnosis of tuberculosis compared to a standard culture method. Furthermore, this device could also be applied for real-time growth monitoring of Mycobacterium tuberculosis in a mycobacterial culture system.

Surface modification of silicon dioxide, silicon nitride and titanium oxynitride for lactate dehydrogenase immobilization.

Three different types of surface, silicon dioxide (SiO2), silicon nitride (Si3N4), and titanium oxynitride (TiON) were modified for lactate dehydrogenase (LDH) immobilization using (3-aminopropyl)triethoxysilane (APTES) to obtain an amino layer on each surface. The APTES modified surfaces can directly react with LDH via physical attachment. LDH can be chemically immobilized on those surfaces after incorporation with glutaraldehyde (GA) to obtain aldehyde layers of APTES-GA modified surfaces. The wetting properties, chemical bonding composition, and morphology of the modified surface were determined by contact angle (CA) measurement, Fourier transform infrared (FTIR) spectroscopy, and scanning electron microscopy (SEM), respectively. In this experiment, the immobilized protein content and LDH activity on each modified surface was used as an indicator of surface modification achievement. The results revealed that both the APTES and APTES-GA treatments successfully link the LDH molecule to those surfaces while retaining its activity. All types of tested surfaces modified with APTES-GA gave better LDH immobilizing efficiency than APTES, especially the SiO2 surface. In addition, the SiO2 surface offered the highest LDH immobilization among tested surfaces, with both APTES and APTES-GA modification. However, TiON and Si3N4 surfaces could be used as alternative candidate materials in the preparation of ion-sensitive field-effect transistor (ISFET) based biosensors, including lactate sensors using immobilized LDH on the ISFET surface.

Increasing active surface area to fabricate ultra-hydrophobic surface by using "Black silicon" with bosch etching process.

Needle-shaped pillars so-called "Black silicon" (B-Si) were fabricated by etching cleaned silicon wafer with fluorine-based deep reactive ion etching plasma. The B-Si pillar with the pillar size (a) and spacing (b) of 250 nm, and height (h) of 6.47 microm, coated with SiOxFy film had water contact angle (WCA) and ethylene glycol contact angle (ECA) of 159.8 degrees and 135.5 degrees, respectively. After coating the pillar with trichloro(1H,1H, 2H,2H-perfluorooctyl)silane (TPFS), the WCA and ECA increased to 166.2 degrees and 161.8 degrees, respectively. At the optimum etching condition, the B-Si pillar with the size a = 376 nm, b = 576 nm, h = 6.47microm, and the aspect ratio of 14.80 showed the WCA and ECA of 4.25 degrees and 14.77 degrees, respectively. After coating with the TPFS, liquid droplets ran across the sample's surface rapidly and the WCA and ECA could not be measured. Moreover, when the pillar height was increased twice, the WCA and ECA of the B-Si with and without the TPFS coating were greater than 170 degrees, indicating excellent water-and-oil repellency and can be applied for Micro-Electro-Mechanical Systems (MEMS).

An effect of silicon micro-nano-patterning arrays on superhydrophobic surface.

Superhydrophobic surface can be fabricated by creating a rough surface at very fine scale and modify it with low-surface energy material. To obtain the optimum superhydrophobicity, the surface roughness must be maximized. To avoid the limitation of scaling down the pattern size by using an expensive lithography tools, the surface roughness factor (r) was increased by means of changing an asperity shape so as to increase its overall surface area. In this paper, the patterns of the asperities under studied were wave stripes, line stripes, cylindrical pillars, square pillars, pentagonal pillars, hexagonal pillars, and octagonal pillars. All pillar shapes were arranged in square arrays, hexagonal arrays, and continuous stripes. The asperities sizes and the pitches were varied from 1 to 5 microm with 10 microm of asperity height. Then the patterned surfaces were coated with polydimethylsiloxane mixed with 10 wt% dicumylperoxide. It was found that the stripe asperities can generate only hydrophobic surface with water contact angle (WCA) of 135 degrees to 145 degrees. The pillars with square and hexagonal arrays had the WCA of 149 degrees to 158 degrees. The pentagonal pillars with square and hexagonal arrays achieved the highest WCA with an average WCA of 156 degrees. It was evident that the pillar shape had significant effect on the superhydrophobicity.