title: Microfluidic immunosensor for rapid and highly-sensitive salivary cortisol quantification.
abstract: This paper presents a novel poly(dimethylsiloxane) (PDMS) microfluidic immunosensor that integrates a complementary metal-oxide-semiconductor (CMOS) optical detection system for a rapid and highly-sensitive quantification of salivary cortisol. The simple and non-invasive method of saliva sampling provides an interesting alternative to the blood, allowing a fast sampling at short intervals, relevant for many clinical diagnostic applications. The developed approach is based on the covalent immobilization of a coating antibody (Ab), a polyclonal anti-IgG, onto a treated PDMS surface. The coating Ab binds the capture Ab, an IgG specific for cortisol, allowing its correct orientation. Horseradish peroxidase (HRP)-labelled cortisol is added to compete with the cortisol in the sample, for the capture Ab binding sites. The HRP-labelled cortisol, bonded to the capture Ab, is measured through the HRP enzyme and the tetramethylbenzidine (TMB) substrate reaction. The cortisol quantification is performed by colorimetric detection of HRP-labelled cortisol, through optical absorption at 450nm, using a CMOS silicon photodiode as the photodetector. Under the developed optimized conditions presented here, e.g., microfluidic channels geometry, immobilization method and immunoassay conditions, the immunosensor shows a linear range of detection between 0.01-20ng/mL, a limit of detection (LOD) of 18pg/mL and an analysis time of 35min, featuring a great potential for point-of-care applications requiring continuous monitoring of the salivary cortisol levels during a circadian cycle.
authors.affiliation: Microelectromechanical Systems Research Unit (CMEMS-UMinho), University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal.
authors.forename: V
authors.initials: V
authors.lastname: Pinto
authors.affiliation: Microelectromechanical Systems Research Unit (CMEMS-UMinho), University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal.
authors.forename: P
authors.initials: P
authors.lastname: Sousa
authors.affiliation: Microelectromechanical Systems Research Unit (CMEMS-UMinho), University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal.
authors.forename: S O
authors.initials: SO
authors.lastname: Catarino
authors.affiliation: Life and Health Sciences Research Institute (ICVS), School of Medicine, Portugal; ICVS/3B's, PT Government Associate Laboratory, University of Minho, Braga/Guimarães, Portugal.
authors.forename: M
authors.initials: M
authors.lastname: Correia-Neves
authors.affiliation: Microelectromechanical Systems Research Unit (CMEMS-UMinho), University of Minho, Campus de Azurém, 4800-058 Guimarães, Portugal. Electronic address: gminas@dei.uminho.pt.
authors.forename: G
authors.initials: G
authors.lastname: Minas
mesh_terms: D000888:Antibodies, Anti-Idiotypic / Q000737:chemistry / Q000276:immunology; D015374:Biosensing Techniques / Q000379:methods*; D006046:Gold / Q000737:chemistry; D006735:Horseradish Peroxidase / Q000737:chemistry; D006801:Humans; D006854:Hydrocortisone / Q000737:chemistry / Q000302:isolation & purification*; D007118:Immunoassay / Q000379:methods; D053768:Metal Nanoparticles / Q000737:chemistry*; D044085:Microfluidics / Q000295:instrumentation; D012463:Saliva / Q000737:chemistry*
chemical_list: D000888:Antibodies, Anti-Idiotypic; C048844:anti-IgG; D006046:Gold; D006735:Horseradish Peroxidase; D006854:Hydrocortisone
keywords: Colorimetric detection; Lab-on-a-chip (LOC); Microfluidic immunosensor; Poly(dimethylsiloxane); Salivary cortisol