We all hate waiting for tests results, especially when it comes to medical tests where the uncertainty of not knowing what’s wrong can be a real worry. As a result, the development of diagnostic tests that can be performed wherever the patient is, whether that is at home, in a doctor’s surgery or in a medical centre in the developing world, obtaining almost instantaneous results is a current hot topic. Over the past few years, a wide range of point-of-care diagnostic platforms have been developed and the field holds tremendous potential, perhaps one day eliminating the need for laboratory-based diagnostic tests altogether.
Hua-Zhong Yu from Simon Fraser University in Canada and colleagues from Biogate Laboratories, Canada, and Taiyuan University of Technology, China, have taken a step forward in this field by developing a diagnostic platform that is based on standard DVD technology. The system involves an immunoassay, where antibodies capture and detect the analyte in question.
First, video data is burned onto a standard re-writable DVD. Antibodies that bind to the analyte to be measured are then attached to the polycarbonate surface of the DVD via a surface modification step. The sample is loaded, the analyte is captured and any excess material is washed away. Next, another set of antibodies that will bind the analyte are added. The DVD is washed with silver nitrate solution and gold nanoparticles conjugated to the most recently added antibodies promote the reduction of silver ions into metallic silver and hey presto, silver particles are formed on the surface of the DVD that will interrupt the laser reading process when you try and play it. Commercially available quality control software can be used to measure the number of reading errors on the disk, which is proportional to the amount of analyte in the sample.
The platform has the potential to be used for a wide range of different diagnostic tests, but the team chose to demonstrate the effectiveness of the system by measuring the concentration of human chorionic gonadotropin (hCG) in urine samples. hCG is a hormone produced during pregnancy and so the team effectively created an on-disc pregnancy test. Of course, pregnancy tests are already widely available at relatively low cost, but the key advantage of this system is that it is quantitative. As a result, it can do much more than just giving you a yes or no indication of whether or not you’re pregnant. For example, the system could warn of preeclampsia or check the progression of testicular cancer – these quantitative hCG tests are currently performed in specialist laboratories.
‘The researchers have picked up on a striking benefit of centrifugal microfluidic platforms,’ says Jens Ducrée, an expert in point-of-care diagnostic devices from Dublin City University in Ireland, ‘that is, that bioassays may be read out, even in a quantitative fashion, by means of commodity optical disc drives such as CD and DVD players.’
Yu and colleagues are now working to optimise and commercialise their DVD-based diagnostic platform.
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