Design of nanoporous metals with bimodal pore size distributions for enhanced biosensing

Nanoporous gold (np-Au) has shown great potential in catalysis, plasmonics, sensing, etc. In this work, by two-step dealloying a well-designed AuAgAl ternary precursor alloy, np-Au with bimodal ligament/pore size distributions is successfully fabricated. The first dealloying in HCl solution removes Al and generates a nanoporous AuAg alloy which would be mildly annealed at 200°C for 30 min to homogenize the alloy ligament and enlarge the ligament/pore size. Next, the nanoporous AuAg alloy is further dealloyed in a HNO₃ solution to etch Ag and fabricate np-Au with a hierarchical microstructure. This novel bimodal np-Au is demonstrated to exhibit enhanced electrocatalytic activity towards H₂O₂ reduction and be a better support for the fabrication of an oxidase-based biosensor compared with normal np-Au, with a uniform pore/ligament size of 30-40 nm. In a proof-of-concept study, a sensitive glucose biosensor with a linear range up to 21 mM is fabricated by immobilization of glucose oxidase on the bimodal np-Au.