Quantitative Lateral Flow Assays for Salivary Biomarker Assessment: A Review.

Saliva is an emerging biofluid with a significant number of applications in use across research and clinical settings. The present paper explores the reasons why saliva has grown in popularity in recent years, balancing both the potential strengths and weaknesses of this biofluid. Focusing on reasons why saliva is different from other common biological fluids such as blood, urine, or tears, we review how saliva is easily obtained, with minimal risk to the donor, and reduced costs for collection, transportation, and analysis. We then move on to a brief review of the history and progress in rapid salivary testing, again reviewing the strengths and weaknesses of rapid immunoassays (e.g., lateral flow immunoassay) compared to more traditional immunoassays. We consider the potential for saliva as an alternative biofluid in a setting where rapid results are important. We focus the review on salivary tests for small molecule biomarkers using cortisol as an example. Such salivary tests can be applied readily in a variety of settings and for specific measurement purposes, providing researchers and clinicians with opportunities to assess biomarkers in real time with lower transportation, collection, and analysis costs, faster turnaround time, and minimal training requirements. We conclude with a note of cautious optimism that the field will soon gain the ability to collect and analyze salivary specimens at any location and return viable results within minutes.

Salivary cortisol results obtainable within minutes of sample collection correspond with traditional immunoassays.

PURPOSE: Cortisol is frequently assayed as a stress-responsive biomarker which changes over the course of minutes to meet the demands of a person's social context. Salivary cortisol is often used as a noninvasive sampling method that possesses important health implications. A critical barrier to psychobiological research that involves salivary cortisol is a time delay of days to months before cortisol results are obtained via immunoassay, long after the person is no longer proximate to the social context in which they provided the sample. The present study was designed to address this critical barrier through creation of a lateral flow test (LFT) cortisol device capable of measuring salivary cortisol within minutes of sample collection. The LFT is frequently used within commercial point-of-care settings to obtain rapid answers to the presence/absence of a biomarker. The present study extends the LFT into the research domain by presenting performance characteristics of a quantitative LFT that measures salivary cortisol within 20 minutes of sample collection. METHODS: Saliva samples from 29 adults (15 men) were obtained in the morning and afternoon by using Passive Drool and then the Super·SAL Extra Collection Device (hereafter Super·SAL) and later assayed with LFT and a commercially available enzyme immunoassay. FINDINGS: Results indicate the LFT correlated well with these collection methods (R = 0.872 with Super · SAL, R = 0.739 with Passive Drool, P < 0.0001) and at comparable levels to correspondence of Super · SAL with Passive Drool (R = 0.798, P < 0.0001) which were measured with the same assay. IMPLICATIONS: These results open an exciting new possibility to integrate this technologic advance into stress research, including knowing and potentially changing the person's social context in a time-sensitive manner. Methodological improvements such as this have the possibility of refining conceptual models of stress reactivity and regulation.

RNAPro•SAL: a device for rapid and standardized collection of saliva RNA and proteins.

The stabilization and processing of salivary transcriptome and proteome biomarkers is a critical challenge due to the ubiquitous nature of nucleases and proteases as well as the inherent instability of these biomarkers. Furthermore, extension of salivary transcriptome and proteome analysis to point-of-care and remote sites requires the availability of self-administered ambient temperature collection and storage tools. To address these challenges, a self-contained whole saliva collection and extraction system, RNAPro•SAL, has been developed that provides rapid ambient temperature collection along with concurrent processing and stabilization of extracellular RNA (exRNA) and proteins. The system was compared to the University of California, Los Angeles (UCLA) standard clinical collection process (standard operating procedure, SOP). Both systems measured total RNA and protein, and exRNA IL-8, glyceraldehyde 3-phosphate dehydrogenase (GAPDH), ß-actin and ribosomal protein S9 (RPS9) by qPCR. Proteome analysis was measured by EIA analysis of interleukin-8 (IL-8), and ß-actin, as well as total protein. Over 97% of viable cells were removed by both methods. The system compared favorably to the labor-intensive clinical SOP, which requires low-temperature collection and isolation, yielding samples with similar protein and exRNA recovery and stability.