Paper-based biosensors featuring immunoconjugated gold nanoparticles have gained extraordinary momentum in recent times as the platform of choice in key cases of field applications, including the so-called rapid antigen tests for SARS-CoV-2. Here, we propose a revision of this format, one that may leverage on the most recent advances in materials science and data processing. In particular, we focus on an amplifiable DNA rather than a protein target, and we assess the replacement of gold nanospheres with anisotropic nanorods, which are about 10-fold brighter and multiplexable.
By comparison with a gold-standard method for dot-blot readout with digoxigenin, we show that gold nanorods entail much faster and easier processing, at the cost of a higher detection limit (from below 1 to 10 ppm in the case of plasmid DNA containing a target transgene). In addition, we test a complete workflow for systematic acquisition and machine-learning regression of photographs of dotblot membranes as a tool to gain more analytical sensitivity and potential for quantification. A leaveone-out strategy for training and validation with as few as 36 sample instances already improves the detection limit reached by the naked eye by a factor around 2.
Taken together, we conjecture that the synergistic combination of new materials and innovative tools for data processing may bring the analytical sensitivity of paper-based biosensors to approach the level of lab-grade molecular tests.