# Paper and Fiber-Based Bio-Diagnostic Platforms: Current Challenges and Future Needs
## 2 Major Challenges and Opportunities
### Shelf Life of the Paper/Fiber Materials  
Apart from the efficiency of the developed platforms, the reproducible shelf life of the products is also of a great importance. With the significant advances in the fabrication of paper-based devices, the resulting paper products remain sensitive materials, with low tensile strength, and high vulnerability to modulations in environmental conditions, particularly temperature and humidity [3; 54; 55]. Table 4 summarizes the shelf life details of some of the conventional, commercial, and novel paper/fiber materials. Researchers face challenges maintaining the shelf life of the commonly used paper materials (e.g., porous cellulose and nitrocellulose) even prior to the application of surface modification techniques [54; 55]. Porous cellulose products such as Ahlstrom A-55 and Whatman CHR (chromatography) # 1 can provide reproducible results for at least five weeks if it is stored at 4 \({}^{\circ}\)C under sealed conditions (Table 4) [54; 55]. The shelf life of nitrocellulose and nylon materials is reported to be approximately 3 and 7 months, respectively [110; 111]. Fiber substitutes, such as polyhydroxybutyrate (PHB) and poly(3-hydroxyrate-co-3-hydroxyvalerate) (PHBV), however, are reported to be more stable towards temperature change and possess relatively high degradation temperatures (Table 4) [112; 113; 114; 115; 116]. \begin{table}
\begin{tabular}{c c c c} \hline \hline \multicolumn{2}{c}{**Type of Paper/Fiber**} & \multicolumn{1}{c}{**Self Life/Stability**} & **Ref. ** \\ \hline \multirow{6}{*}{**Conventional and commercial materials**} & \multirow{6}{*}{Whatman CHR \# 1} & Lab-en-paper immunous-devices, constructed with this material can provide reproducible results upon storage at 4°C (called for last 8 weeks [54]. In other studies on antibody immobilization on the surface of this material, the stability decreased with increasing temperature and relative humidity (RI) [60]. All-five were more than 10 days) and was dependent on relative humidity (RI) [61]. However, at 80°C, the half-life \\ \cline{2-4}  & & varied from -3 days at low RI loss than half about about about 90°R [61]. & [55] \\ \cline{2-4}  & \multirow{6}{*}{Nitrocellulose} & The material is commonly used in later low-rays. For the detection of \(T\) _transiliensis_ B-339 antigen, 91\% sensitivity and 95\% specificity was reported, while the membrane & [110] \\ \cline{2-4}  & & have reported to be variable for use in at least 90 days after verification, & \\ \cline{2-4}  & \multirow{6}{*}{Nylon} & The stability of nylon membranes is relatively high [10]. Imregulated protein in the network of nylon has the shelf life several months (at least 2 months) with minimal loss in activity, the immobilized enzymes with nylon's structure remain active for at least 33 h without significant loss of activity [111]. & [37,111] \\ \cline{2-4}  & \multirow{6}{*}{Whatman \# 903} & The  
Apart from the bio-receptive material itself, the duration in which the impregnated proteins in the structure of the papers/fibers remain active is vital. Higher stability of the biomolecules and a longer shelf life for the developed materials permits the long-distance transportation of the platforms to where they are mostly needed, under-privileged areas. Immobilized antibodies in the network of porous cellulose (Whatman CHR # 1 and Ahlstrom A-55) were found to lose their activity with increasing temperature (\(\sim\)40 \({}^{\circ}\)C) while the stability of the impregnated product over time was significantly affected with an increase in relative humidity (RH) (Table 4) [54; 55]. Other studies have established that antibodies can remain active for a long period under optimal storage conditions (\(-\)20 \({}^{\circ}\)C) if impregnated using a dry-reagent technique [67; 119]. Papers are often harshly affected by the treatment processes, which may make them even more sensitive than in their original states.