Optical protein sensor for detecting cancer markers in saliva

Abstract

A surface immobilized optical protein sensor has been utilized to detect Interleukin-8 (IL-8) protein, an oral cancer marker, and can reach limit of detection (LOD) at 1.1 pM in buffer without using enzymatic amplification. Only after applying enzymatic amplification to increase the signal level by a few orders of magnitude, ELISA can reach the LOD of 1pm level. We then develop the confocal optics based sensor for further reducing the optical noise and can extend the LOD of the surface immobilized optical protein sensor two orders in magnitude. These improvements have allowed us to detect IL-8 protein at 4.0 fM in buffer. In addition, these sensitive LODs were achieved without the use of enzymatic signal amplification, such that the simplified protocol can further facilitate the development of point-of-care devices.The ultra sensitive optical protein sensor presented in this paper has a wide number of applications in disease diagnoses. Measurements for detecting biomarkers in clinical sample are much more challenging than the measurements in buffer, due to high background noise contributed by large collections of non-target molecules. We used clinical salvia samples to validate the functionality of the optical protein sensor. Clinical detection of disease-specific biomarkers in saliva offers a noninvasive, alternative approach to using blood or urine. Currently, the main challenge of using saliva as a diagnostic fluid is its inherently low concentration of biomarkers. We compare the measurements of 40 saliva samples; half from oral cancer patients and half from a control group. The data measured by the optical protein sensor is compared with the traditional Enzyme-Linked Immunosorbant Assay (ELISA) values to validate the accuracy of our system. These positive results enable us to proceed to using confocal optical protein sensor to detect other biomarkers, which have much lower concentrations.

Microspectroscopic SERS detection of interleukin-6 with rationally designed gold/silver nanoshells

“…Improved detection limits have been reported for uorescence 34 and surface plasmon resonance (SPR) sensing. 35 SERS, however, offers the additional unique spectral multiplexing advantage.…”

Reading cancer-specific signatures

“…1 The other is an electrochemical DNA sensor 2,3 that exploits a steric hindrance scheme to suppress nonspecific signals.…”

“…By combining electric field control with hairpin probes, the limit of detection for RNA is about 0.4fM, which is 10,000-fold more sensitive than conventional linear probes. 1,3 By extending the sensitivity of these techniques, without the need for enzymatic amplification steps, we have expanded the range of detection for these biosensors while maintaining their simplicity. The resultant methods are well suited for point-ofcare detection of specific biomarkers within complex bodily fluids such as saliva and are a significant advance toward routine molecular diagnostics in the clinical setting.…”

Microfluidic optoelectronic sensor for salivary diagnostics of stomach cancer

“…Salivary diagnostics is much more convenient than biopsy or blood test: sample collection is simple, non-invasive and, therefore, not painful (Martin et al, 2012;Soini et al, 2010;Streckfus and Bigler, 2002). With respect to the gastric cancer screening, saliva is commonly analyzed for the presence of abnormal genetic material, or of specific biomarkers, which are detected by analyte-specific interactions using immunoassay arrays (Ivnitski et al, 2004;Jokerst et al, 2009;Tan et al, 2008). While these techniques are effective in early detection of gastric cancer, they are less appropriate for fast and high throughput screening, particularly outside of medical facilities.…”