## Appendix A Supplementary Section
### Sandwich ELISA Procedure  
Step 1. Each well of i-ELISA was filled with 100 \(\upmu\)L of capture antibody (Ab), rabbit anti-dengue virus 2 antibody (ab155042, Abcam, San Francisco, CA, USA) diluted (1:500) in coating buffer. Coating buffer was prepared by mixing 0.85 g of sodium chloride (NaCl, Sigma, San Antonio, TX, USA), 0.14 g of disodium phosphate (Na\({}_{2}\)HPO\({}_{4}\), Sigma, San Antonio, TX, USA), and 0.02 g of monosodium phosphate (NaH\({}_{2}\)PO\({}_{4}\), Sigma, San Antonio, TX, USA) in 100 mL of phosphate-buffered saline (PBS, Fisher Scientific, Waltham, MA, USA) with the pH of 7.4. Incubation was carried out for 2 h at 37 \({}^{\circ}\)C.  
Step 2. Washing step was performed by charging each well with 200 \(\upmu\)L of washing buffer which consists of 0.05% Tween 20 (Sigma, San Antonio, TX, USA) in PBS solution (pH = 7.4). This step was performed at room temperature three times (each time 5 min) by using a shaker with the shaking speed of 1000 rpm. The exact same process was performed between each two steps of the sandwich assay. It is important to note that the lid was placed on top of well plate not only during the washing steps but also throughout all different steps of the sandwich ELISA. Therefore, paper segments of i-ELISA have been directly in contact with the respective buffers in the conducted incubations.  
Step 3. The blocking step was performed in order to achieve high selectivity and to avoid non-specific bindings. This step was conducted by charging each well with 100 \(\upmu\)L of blocking buffer and incubating well plates at 37 \({}^{\circ}\)C for 1 h. Blocking buffer was prepared by adding 1 g of bovine serum albumin (BSA, Sigma, San Antonio, TX, USA) to 100 mL of washing buffer. Blocking buffer used in the assay had a controlled pH of 7.4.  
Step 4. Each well of i-ELISA was charged with 100 \(\upmu\)L of the diluted virus solution and incubation lasted for 2 h at 37 \({}^{\circ}\)C. Virus solution was prepared by the serial dilution method in a variety of different concentrations depending on the application of the assay.  
Step 5. Primary Ab solution was prepared by diluting mouse IgG2a anti DV (ab155863, Abcam, San Francisco, CA, USA) in diluting buffer (DB) with the ratio of 1:200 (Ab:DB). Diluting buffer was made by adding 0.4 g of BSA, 4 mL of PBS buffer and 120 \(\upmu\)L of Trintonx-100 into 36 mL of distilled water at the pH of 7.4. Each well received 100 \(\upmu\)L of primary Ab solution and well plates were placed in the incubator of 37 \({}^{\circ}\)C for 2 h.  
Step 6. The last incubation was carried out by adding 100 \(\upmu\)L of secondary antibody solution that was also diluted in diluting buffer (1:500). Anti-mouse igG2a alkaline phosphatase (ab97242, Abcam, San Francisco, CA, USA) was used as the secondary Ab. This step was performed at the temperature of 37 \({}^{\circ}\)C for 30 min.  
Step 7. In the final step, wells were thoroughly washed and charged with 100 \(\upmu\)L of mixed substrate (alkaline phosphatase blue microwell substrate, components A and B). This reaction was conducted at ambient temperature and stopped after 15 min by adding 100 \(\upmu\)L of alkaline phosphatase stopping solution (A585, Sigma, San Antonio, TX, USA). Signal intensity was recorded by using Bio-Rad ELISA reader (model 680) at the specific wavelength of 570 nm as the manufacturing guideline has suggested.