Pockets of Gold and Silver

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Science  30 Jan 2004:
Vol. 303, Issue 5658, pp. 593
DOI: 10.1126/science.303.5658.593b

In the adaptation of technologies for use in the developing world or for broad use by first-line emergency responders, it is key that they be low-cost and require minimal supporting infrastructure and personnel. With these two principles in mind, Sia et al. have designed a portable, cost-effective immunoassay with sensitivities and detection limits comparable to those of the standard enzyme-linked immunosorbent assay (ELISA). Instead of linking amplifying enzymes to the antibodies, the authors attached 10-nm colloidal gold particles, which in the presence of hydroquinone reduced silver ions to silver, which then catalyzes the reduction reaction. The silver film produced is easily and quantitatively detected with a low-power laser diode. By operating the light source in a pulsed mode, it was possible to filter out ambient light, even outdoors. The platforms for the detectors were fabricated with soft lithography, and both microwell plates and microfluidic channels could be used. Although microfluidic ELISA runs into detection problems because of enzyme product diffusion, this is not observed with the colloidal gold antibodies. — MSL

Angew. Chem. Int. Ed. 43, 498 (2004).

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