Detection of picomolar levels of interleukin-8 in human saliva by SPR

Abstract

Researchers at UCLA have discovered that the levels of interleukin-8 (IL-8) protein in the saliva of healthy individuals and patients with oropharyngeal squamous cell carcinoma (OSCC) are 30 pM and 86 pM, respectively. In this study, we present the development of the first immunoassay for the quantification of picomolar IL-8 concentrations in human saliva using Biacore surface plasmon resonance (SPR) in a microfluidic channel. A sandwich assay using two monoclonal antibodies, which recognize different epitopes on the antigen (IL-8), was used. Only 13 minutes were required to determine the quantity of pure IL-8 added to just 100 microL of either buffer or saliva-based samples. The limit of detection (LOD) of this immunoassay in buffer was 2.5 pM, and the precision of the response for each concentration was <3% of the coefficient of variation. When first analyzing the saliva supernatants, non-specific binding to the surface was observed. By adding carboxymethyl dextran sodium salt (10 mg mL(-1)) to compete with the surface dextran and primary antibody for non-specific interactions, the signal to noise ratio was greatly improved. The LOD of this immunoassay in saliva was 184 pM. A minimum concentration of 250 pM of exogenous IL-8 could then be consistently detected in a salivary environment. The precision of the response for each IL-8 concentration tested was <7% of the coefficient of variation. Diagnostic sensitivity for oral cancer can be achieved by pre-concentrating the saliva samples 10 fold prior to SPR analysis, making the target levels of IL-8 300 pM for healthy individuals and 860 pM for oral cancer patients.

Biofunctionalized Nanostructured Zirconia for Biomedical Application: A Smart Approach for Oral Cancer Detection

“…In this context, the biomarkers, such as interleukin‐8 (IL‐8), interleukin‐6 (IL‐6), vascular endothelial growth factor (VEGF) and epidermal growth factor receptor (EGFR) are currently being used for detection of oral cancer 14, 15, 16, 17. The OC detection via these biomarkers is currently a challenge since these are secreted at very low concentration (≈pg mL −1 ) and the biosensors proposed for the detection of these biomarkers require serum samples and are thus invasive 14, 15, 16, 17. Thus, detection of OC biomarkers in human saliva samples provides a noninvasive and pain‐free alternative.…”

“…Efforts have been made for the detection of OC utilizing biosensor platforms 14, 15, 16, 17. Yang et al reported electrochemical biosensor for the detection of trace level of salivary IL‐8 protein 15.…”

“…Yang et al reported electrochemical biosensor for the detection of trace level of salivary IL‐8 protein 15. To achieve low level of detection, streptavidin and HRP labeling of the receptor biomolecules has been proposed which increases the complexity of detection 15.…”

Silicon Nanowire Biosensor for Highly Sensitive and Multiplexed Detection of Oral Squamous Cell Carcinoma Biomarkers in Saliva

“…As reported, the LOD of enzyme linked immunosorbent assay (ELISA) for IL-8 in buffer is 1 pM (8.3 pg/mL, the molar molecular weight of IL-8 is 8.3 kDa) and SPR achieves an LOD of 184 pM (1.5 ng/mL ) for IL-8 in human saliva. 39 The LOD of ELISA for TNF-α was reported to be 0.48 pg/mL in the buffer. 40 Compared with other biosensors for the detection of IL-8 or TNF-α, our method has not only better sensitivity, but also multiplexed detection ability.…”

“…9 However, the concentration of the biomarkers in saliva is much lower than that in the blood, and the salivary environment is more complicated, revealing that a sensitive and multiplexed detection method for biomarkers is highly required. 10 These biosensors based on the labeling of biomolecules with tags, such as radioactive isotope, quantum dots or fluorescent dyes, have been applied for the detection of disease biomarkers. [11][12][13][14] Although these label-based methods have good sensitivity, they suffer from some drawbacks, including challenges concerning the labeling procedures, tedious and time-consuming experimental procedures, thereby hindering them from more extensive applications.…”