Paper substrates are gaining increasing attention in biodiagnostics, food quality testing, environmental monitoring, flexible energy and electronic devices owing to the numerous advantages such as high specific surface area, excellent wicking properties, compatibility with conventional printing approaches, significant cost reduction and easy disposability. Recent surge in the activity related to paper-based diagnostic devices is primarily focused on realizing microfluidic paper-based analytical devices (µPADs) for point-of-care assays and inexpensive diagnostic tools for resource-limited environments. Most of these developments rely on labour, time and resource-intensive patterning techniques such as photolithography, wax printing, inkjet printing of polydimethylsiloxane (PDMS), to create fluidic pathways and/or differential functionalization of predetermined regions for site-selective adsorption of the biochemical reagents.
Here we demonstrate simple yet powerful “pen-on-paper” approach for realizing multiplexed label-free bioassays using a regular ball pen filled with gold nanorods or biofunctionalized gold nanorods as (bio)plasmonic ink. Pen-on-paper plasmonic biosensors offer two distinct advantages over plasmonic paper substrates obtained using immersion method as reported previously. Firstly, pen-on-paper serves as a facile method to miniaturize the test domain size to few mm2, which significantly improves the sensitivity of the plasmonic biosensor compared to bioplasmonic paper fabricated using immersion approach. Secondly, pen-on-paper using bioplasmonic ink enables simple and efficient multiplexed biodetection of paper substrates thus leading to multi-marker biochips. In this study, we demonstrate these two aspects using gold nanorods as plasmonic nanotransducers.
1. Tian, L., Tadepalli, S., Park, S.H., Liu, K.K., Morrissey, J.J., Kharasch, E.D., Naik, R.R., Singamaneni, S. (2014) Bioplasmonic calligraphy for multiplexed label-free biodetection. Biosens. Bioelectron. 59, 208.