Fig. 3: Substrate treatment and biosensing assessment.

a The substrate is assembled in layers from bottom to top: a glass slide, double-sided tape, PI film, silicon adhesive, and a hydrophilic nanofibrous PTFE membrane (see Figure S18 for SEM). Thermal treatment modulates the membrane’s wettability by evaporating silicone nanoparticles from the adhesive layer. These nanoparticles attach to the nanofibers, thereby altering the surface properties. b Fluorescent image of the deposited fluorescent dyes for a sample droplet deposited on the membrane under different temperatures. By increasing the temperature, the coffee-ring (CR, dashed orange line) shrinks and moves away from the spreading line (SL, dashed gray line) to enable the desirable high pre-concentration results below a critical temperature. Above the critical temperature, the formation of crystalline objects at the coffee-ring prevents GNShs to access biomarkers (SL and CR lines coalesce at the same position). c The distance between the spreading line and the coffee-ring is defined as the spreading variation. The spreading rate (red color symbols) and maximum spreading distance (blue color symbols) vs. applied temperature shows 80 ^oC is the critical thermal treatment temperature of the prototype system as the membrane wettability decreases significantly to reduce the spreading of the droplet. d Experimental results of the evaporation time (red color symbols) and contact angle (blue color symbols) vs. temperature. It is found that the contact angle increases significantly above 80 ^oC implying more hydrophobic behavior. The evaporation time increases with the temperature, since higher thermal treatment leads to less spreading and more solution stays inside the residual droplet, leading to less available surface area for the evaporation. Results are presented as mean values ± SD, based on n = 3 measurements, except contact angle data which is based on the instrument repeatability. e The asymmetric patterns for the PSA protein. By reducing the PSA concentration, the intensity of the specific pattern decreases. Below the LOD, specific and non-specific patterns resemble the control sample (pure buffer). Key features, such as pattern intensity, gradient, higher-order statistics, and coffee-ring intensity, provide both qualitative and quantitative results. Sensing experiments were repeated at least three times.