tons of waste in 2005 in EU, and it is expected to grow to more than 12. The interest in μPADs has led to a number of excellent comprehensive reviews in the field in this review, we do not attempt to reference the entire field but instead seek to highlight major developments as well as areas that will be important for future development of this field.Įlectronic equipment generated 9. The ability to carry out multiplexed analysis without external pumps using inexpensive, disposable devices makes μPADs ideal for point-of-care (POC) analysis. Furthermore, because the devices are made from cellulose or modified cellulose using inexpensive manufacturing methods, the devices can be inexpensive and disposable. μPADs address these problems by patterning paper to create microfluidic channel networks that can direct flow to different regions of the device without the need for external pumps used in most traditional microfluidic devices. Cellulose, and modified cellulose, has been used for centuries for making chemical measurements but devices made with this material traditionally suffered from either poor detection limits and/or limited ability to provide quantitative measurements. The interest in and use of microfluidic paper-based analytical devices (μPADs) has grown exponentially over the last decade. Specifically, the results showed that the HBCL having the alkyl chain is chemically stable for at least 90 days, making it the preferred cross-linker for bioassays. Finally, we found that the stability of the HBCLs themselves was related to the nature of their spacer arms. We also demonstrated that the AgNP-HBCL-Ab conjugates were stable and active for at least 2 weeks. This finding confirmed that the HBCLs exerted orientational control over the Abs. Electrochemical results, obtained using a half-metalloimmunoassay, proved that Abs conjugated to AgNPs via either of the two HBCLs were 4 times more active than those conjugated by the more common physisorption technique. Both cross-linkers immobilized 5 ± 1 Abs on the surface of each 20-nm-diameter AgNP. The two HBCLs differed in two respects, however: (1) either a thiol or a dithiolane group was used for attachment to the AgNP and (2) the spacer arm was either a PEG chain or an alkyl chain. Two HBCLs, each having a hydrazide terminal group, were synthesized and tested for effectiveness. A hydrazone conjugation method resulted in exclusive modification of the polysaccharide chains present on the fragment crystallizable region of the Abs, leaving the antigen-binding regions accessible. Here we report on the use of heterobifunctional cross-linkers (HBCLs) to control the number, orientation, and activity of immunoglobulin G antibodies (Abs) conjugated to silver nanoparticles (AgNPs).
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