# Paper and Fiber-Based Bio-Diagnostic Platforms: Current Challenges and Future Needs
## 2 Major Challenges and Opportunities
### Easy Operation for Onsite Health Check  
Even though the majority of paper/fiber-based platforms are aimed at hand-held diagnosis, sample collection and preparation for such devices may introduce considerable challenges. The necessity for sample processing steps, such as separation (e.g., whole blood, serum, and plasma), mixing, adding reagents, and washing among others, falls short of the principles of user-friendliness [38]. In the case of whole blood, specific components/proteins must be removed from the sample to increase the sensitivity and specificity of detection [155]. Normally, plasma should be separated from the whole blood prior to the measurements to minimize errors related to light scattering, absorption, hemolysis, or coagulation of the red blood cells [40]. In the ideal case of a test system, no sample preparation, system calibration, data interpretation, or calculation for end users should be expected [38]. In reality, however, even in well-equipped laboratories, sample preparation suffers from various shortfalls, such as inhomogeneity and the variable viscosity of the samples, as well as presence of interfering agents [3]. The most error-prone aspect of diagnostic tests in laboratories is known to be the pre-analytical phase (sample processing) that includes blood tube sorting, centrifugation, cap removal, sample aliquoting, and recapping [40]. A number of techniques have been developed to offer analysis by individuals with minimal training outside centralized laboratories, such as in doctor's offices, emergency rooms, ambulances, etc. In the context of onsite POC/EPOC and for the technologies to be broadly accepted by the end users in remote/rural areas or elderly people, clear results have to be obtained without the need of any additional processing or external instrument.  
High throughput systems incorporated into the paper-based devices have automated the separation step by using a diverse range of solid materials, including beads, microparticles, fiber matrices, and coated tubes and plates [147; 156; 157; 158; 159; 160; 161; 162; 163]. Additionally, application of pre-depositing agglutination antibodies, concentrated salt solution for blood cell deformation and filtering via paper pores using capillary force are known to be effective techniques for sample separation [164; 165; 166]. In the case of paper strips, the platforms generally contain segments that are designed for automated mixing of the specimen with dry reagents [40; 158]. In such devices, a manual step is normally required to finalize the sample separation. More sophisticated platforms, which enable automation of several sample preparation steps without manual intervention have also been reported. While offering beneficial features, such as automated multistep assays, generally the result is an enlargement of the device dimensions and additional material costs [167; 38; 168]. Readers are recommended to study the excellent reviews by [PERSON] et al., 2017 and [PERSON], 2001 for detailed information [38; 40]. In nucleic acid analysis, sample preparation comprises labor-intensive multiple steps, including suspension, mixing, centrifugation, washing, and elution of the nucleic acids, that are generally performed in dedicated laboratories to minimize cross-contamination and the generation of false positive results [40; 169].  
According to the Clinical Laboratory Improvement Amendments (CLIA) guidelines (formulated by the U.S. Food & Drug Administration (FDA), any user with a 7 th-grade English level should be able to readily operate the diagnostic devices aimed for application outside laboratories after following the instructions provided by the manufacturer [38; 170]. Despite advances in sample preparation and fluidics handling, there is obviously considerable room for improvements in the commercialization of more user-friendly devices.