Table 1.

Paper substrates, their characteristics, and applications.

Paper substrate	Characteristics	Applications
Whatman paper # 1	It is composed of cotton cellulose. The size of pores is 11 μm [30]. Its thickness is 180 μm. It has medium retention and flow rate	It is the most widely used filter paper due to its compatibility with the majority of fabrication methods in μPADS. It is not ideal for all applications [28]. Apilux et. al. have used Whatman paper #1 for creating a device for the determination of gold and iron [31]
Whatman paper # 4	It is made up of cotton cellulose. The size of pores is 20–25 μm. It is a very fast filtering paper [32]. It has an excellent retention rate. The thickness is 210 μm	Li et. al. have used Whatman paper #4 as a substrate for fabricating paper-based microfluidic sensors [33]. Its properties such as larger pore size and higher retention rate were utilized in making paper-based devices
Nitrocellulose membrane	Nitrocellulose membranes have very smooth and uniform pore size, normally 0.45 μm [28]	Lu et. al. have demonstrated a μPAD using nitrocellulose membrane for protein immobilization applications [34]. Nitrocellulose membranes demonstrate a high degree of nonspecific binding toward biomolecules [28]
Bioactive paper	It is obtained by the modification of paper matrix with biomolecules. The biggest advantage of μPADs using bioactive paper is that they do not require sophisticated equipment to operate and are quite simple [35]	Bioactive paper is used in many analytical applications. Pathogen detection is one of them [26]
Cellulose glossy paper	Glossy paper is composed of cellulose but it is blended with certain inorganic fillers. It is non-degradable and a better alternative to filter paper when it is necessary to have the surface modified by the nanoparticles	Arena et. al. have used glossy paper for the fabrication of flexible ethanol sensors at the room temperature [36]