The development of electrochemical sensors as miniaturized and low-cost platforms for the rapid and sensitive detection of biomolecules demands for the requirement of disposable economically viable and easy manufacturable devices. Moreover, it should ASSURES (Affordable, Sensitive, Specific, User-friendly, Robust, Electrode for Sensing) the simple DIY (Do It Yourself) strategy. This could be achievable only if the substrate for the electrodes are inexpensive, easily manufacturable and should be from renewable and reusable resources. Simple paper offers unique advantages such as, easily printable, impregnable, and because of its innate cellulose structures, paper is protein and biomolecules friendly. In addition, porous structure acts as a good filter, and facilitates lateral flow. On the other hand, papers also have been used to make paper analytical devices (PAD), which have the advantages to incorporate microfluidic channels and reagent prestorage zones with mixing opportunities for colorimetric and electrochemical sensing units. Recently, these PADs have been recognized as low-cost and disposable sensing platforms.
Considering the aforementioned properties, herein paper has been explored as a substrate for the fabrication of microfluidic ePAD. Using simple photo-lithography technique, we could achieve the hydrophobic and hydrophilic regions for making a 3 in 1 electrode patterns consists of working, counter and reference electrodes along with the reservoirs for analyte of interests (sample inlet) and reagents (prestorage zones). The designed and fabricated ePAD with colorimetric detection zones (Fig.1) was further characterized by surface morphological and electrochemical studies. As a proof-of-concept, we were able to use ePAD as an electrochemical sensor for trolox (analogue of Vitamin E, an antioxidant), and a probe for selective detection of dopamine in the presence of ascorbic acid. On the other hand, the electrochemical investigations further revealed the interplay between edge plane sites, oxygen functionalities, and the carbon structures π-π interactions with pyrene conjugates towards biomolecules detection. The calibration plot for the trolox sensor showed linear range from 5 µM to 400 µM with a detection limit of (S/N=3) of 1.17 µM. The modified ePAD were able to detect dopamine in real sample with satisfactory results. Aforementioned observations indicated that ePAD have great potential to establish point-of-care testing platform for clinical applications. The findings also demonstrated simple fabrication of microfluidic ePAD is possible, unlike the widely used wax printing technique, and laser scribing or screen printing, or inkjet printing of electrodes onto different substrates, which requires sophisticated instrumentation and skilled personal.
Figure 1
