Low-cost miniaturized UV photosensor for direct measurement of DNA concentration

Highly sensitive measurement of DNA concentration on portable, easy-to-use, low-cost miniaturized equipments without sample waste is challenging.
The DNA peak optical absorbance at λ=260 nm is a well-known property already used in the spectrometric measurement of DNA concentration. Existing apparatus are large-sized, expensive and require a manipulation of DNA. In the current work, a low-power, suitable and miniaturized photosensor aiming at a sensitive and direct measurement of DNA concentration has been designed. Direct measurement, i.e. without sample manipulation, implies UV transmission through the translucid tube wall from the closed tube containing the DNA sample in solution.
To allow measurements at such low wavelengths, we designed and fabricated photodiodes in SOI technology to ensure a high responsivity in the UV range. Measurements of the photodevice confirmed its responsivity spectrum and magnitudes. These fully integrable photodiodes, fabricated in SOI CMOS technology, can be coupled to a complete signal processing microsystem.
Direct measurements at 280 nm optical wavelength of serially diluted DNA within a closed tube (range: 40 pg/μL to 400 ng/μL in a volume of 45 μL) generated a monotonic relation between the DNA concentration and the mean of the diode photocurrent induced by light transmission through DNA solution and tube container. Absorbance of the incident UV ray was inversely proportional to DNA concentration. The photosensor compared favorably with other DNA quantitative methods (spectrophotometry, fluorometry, real-time PCR) in terms of sensitivity.
Originalities of this work are the use of a thin-film SOI photosensor, the low-cost, portable and adaptable system and the potential of the device for direct measurement of nucleic acid concentration within tube containers without sample manipulation or waste.

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