We describe a DNA microarray system using a bipolar integrated circuit photodiode array (PDA) chip as a new platform for DNA analysis. The PDA chip comprises an 8 x 6 array of photodiodes each with a diameter of 600 microm. Each photodiode element acts both as a support for an immobilizing probe DNA and as a two-dimensional photodetector. The usefulness of the PDA microarray platform is demonstrated by the detection of high-risk subtypes of human papilloma virus (HPV). The polymerase chain reaction (PCR)-amplified biotinylated HPV target DNA was hybridized with the immobilized probe DNA on the photodiode surface, and the chip was incubated in an anti-biotin antibody-conjugated gold nanoparticle solution. The silver enhancement by the gold nanoparticles bound to the biotin of the HPV target DNA precipitates silver metal particles at the chip surfaces, which block light irradiated from above. The resulting drop in output voltage depends on the amount of target DNA present in the sample solution, which allows the specific detection and the quantitative analysis of the complementary target DNA. The PDA chip showed high relative signal ratios of HPV probe DNA hybridized with complementary target DNA, indicating an excellent capability in discriminating HPV subtypes. The detection limit for the HPV target DNA analysis improved from 1.2 nM to 30 pM by changing the silver development time from 5 to 10 min. Moreover, the enhanced silver development promoted by the gold nanoparticles could be applied to a broader range of target DNA concentration by controlling the silver development time.

An integrated circuit (IC) bipolar semiconductor photodiode array (PDA) microchip system coupled with light emitting diodes (LEDs) was used for rapid, automated cell viability measurements and high-throughput drug efficacy monitoring. Using the absorption property of trypan blue dye against the red light emitted by LEDs, we determined the effect of three anticancer drugs, viz., camptothecin (CAM), sodium salicylate (Na-Sal) and naringenin (Nar) on the cell viability of human promyelocytic leukemia cells (HL-60) and human embryonic kidney cells (HEK-293). Cell viabilities were measured based on the relative reduction in the photo responses of the photodiodes, covered with known concentration of trypan blue-stained cells. The developed method offers greater sensitivity and hence an excellent estimation of cell viability, but without all the hassle of conventional methods. Flow cytometric measurement and confocal microscopy were applied as complementary techniques for further validation of the results. The work presented here has important implications with regard to high-throughput measurement of optimal concentrations of different drugs against different cell lines in vitro.

A bipolar photodiode array (PDA) protein chip is presented for the detection of E. coli O157:H7. Through unique design of the bipolar PDA microchip, the device was able to detect E. coli O157:H7 directly on the surface of the bipolar PDA. The bipolar PDA microchip maintained low noise level in the entire process of on-chip protein assay and demonstrated high performance of analog signal processing. At every reaction step of the on-chip bioassay, stability of wet photodiode detection elements was confirmed by monitoring the variance of their photosignals with respect to the irradiated red beam. The background signal represented less than 1.8% variance with respect to maximum signal of photodiode detection elements. As a result of using the on-chip bioassay, any complicated optical alignment and components could be removed in the constructed protein chip. This protein chip enables direct optical detection of E. coli O157:H7 eliminating the need of conventional expensive microplate reader that is incompatible with size of sampling platform of protein chip. The independence of the constructed protein chip on conventional microplate reader can contribute greatly to further miniaturization of protein chip and field usable lab-on-a-chip.

No abstract

No abstract