**5. Conclusions**

Saliva is a non-invasive biofluid which is easy to collect, transport, and store. Because of its accessibility and connection to systemic diseases, saliva is one of the best candidates for the advancement of point-of-care medicine, where individuals are able to easily monitor their health status by integrating the salivary diagnostics with suitable biosensing systems. Our present work on the development of a hybrid integrated optical detection based biosensor with integrated micromixing further asserts that colorimetric salivary analysis can be conducted in real time in a dependable, noninvasive, simple, and rapid manner using whole, unprocessed saliva samples with the appropriate chromogenic agents, to screen for any required minerals and metabolite values Thus, this approach could come in handy for real-time point-of-care screening applications for monitoring high-risk hospitalized patients.

**Supplementary Materials:** The following are available online at http://www.mdpi.com/2079-6374/9/2/73/s1: Figure S1: (**A**). (i) Time varying optical absorbance of a saliva sample mixed with chromogenic agen<sup>t</sup> measured on-chip using the hybrid integrated device. The mean optical absorbance value was ~2.36 (ii) Optical absorbance measurement of the same sample measured using a UV/Vis spectrophotometer showing the absorbance value at 450 nm ~2.4. (**B**). Preparation of water in oil emulsion: Finer dispersion of water (blue) in the colorless oil medium throughout the chamber is observed with the actuation of the micromixer. Much longer micromixing time (~600 s) was required to achieve this, Figure S2: Enlarged versions of Figure 2E, Figure 4A,C.

**Author Contributions:** A.C. and M.P. designed the research. V.S. and A.C. conducted the literature review. V.S., T.C., S.M. and A.C. conducted the experiments. A.C., M.P. and S.K. analyzed the results. V.S., A.C., T.C., S.M., S.K. and M.P. prepared the manuscript.

**Funding:** This research was funded by gran<sup>t</sup> provided to A.C. by the College of Engineering (CoE), North Carolina A&T State University (NC A&T SU), and Discovery gran<sup>t</sup> provided to MP by the Natural Sciences and Engineering Research Council of Canada (NSERC). The APC was funded by gran<sup>t</sup> from the CoE, NC A&T SU, provided to AC.

**Acknowledgments:** The authors would like to thank Shyam Aravamudhan, North Carolina Agricultural and Technical State University–Joint School of Nanoscience and Nanoengineering, for generously donating the potassium detection kit. The authors would also like to thank Taylor Mabe for his assistance with the experiments.

**Conflicts of Interest:** The authors declare no conflict of interest.
