Development of biosensors is an active field due to a wide range of applications in lab-on-a-chip, diagnostics of infectious diseases, cancer diagnostics, environment monitoring, biodetection, and others. One of the strategies used for selective identification of a target is to preselect a probe that has a unique affinity for the target, or can uniquely interact or hybridize with the target — a lock and key approach. In this approach, one then needs a platform to support the probe and a recognizing element that can recognize the said interaction between the probe and the target. Electrical readout biosensors have gained much attention because, in principle, they can be made more compact than optical technologies.
Advances in microfabrication and related technologies helped bring the electrical readout-based biosensor development to the forefront. This invention permits a multiple-channel array of nanopipettes to be fabricated, with some control over channel diameter, channel density, channel length, and other parameters of interest. Presently, the nanochannels must be formed one-by-one, or in batches with only a few channels per batch.
The array of nanopipette channels is formed and controlled in a metal-like material that supports anodization. The starting material can be aluminum foil or a thin sheet of aluminum. The film is annealed at 500 °C for three hours. Polishing is done next to reduce surface roughness and obtain a mirror-smooth finish. The finished film is placed in an acid bath (either sulfuric acid or phosphoric acid with pH less than 5) and a direct current is applied. The acid bath needs to be stirred to release the hydrogen bubbles formed. Pore diameter and pore spacing are controlled by the applied potential, the type of acid and its pH, and the bath temperatures. The resulting nanopipette array is suitable to develop a biosensor platform.