Bio-Interface on Freestanding Nanosheet of Microelectromechanical System Optical Interferometric Immunosensor for Label-Free Attomolar Prostate Cancer Marker Detection

Abstract

Various biosensors that are based on microfabrication technology have been developed as point-of-care testing devices for disease screening. The Fabry–Pérot interferometric (FPI) surface-stress sensor was developed to improve detection sensitivity by performing label-free biomarker detection as a nanomechanical deflection of a freestanding membrane to adsorb the molecules. However, chemically functionalizing the freestanding nanosheet with excellent stress sensitivity for selective molecular detection may cause the surface chemical reaction to deteriorate the nanosheet quality. In this study, we developed a minimally invasive chemical functionalization technique to create a biosolid interface on the freestanding nanosheet of a microelectromechanical system optical interferometric surface-stress immunosensor. For receptor immobilization, glutaraldehyde cross-linking on the surface of the amino-functionalized parylene membrane reduced the shape variation of the freestanding nanosheet to 1/5–1/10 of the previous study and achieved a yield of 95%. In addition, the FPI surface-stress sensor demonstrated molecular selectivity and concentration dependence for prostate-specific antigen with a dynamic range of concentrations from 100 ag/mL to 1 µg/mL. In addition, the minimum limit of detection of the proposed sensor was 2,000,000 times lower than that of the conventional nanomechanical cantilevers.

Membrane-Based NEMS/MEMS Biosensors

“…50−52 In addition, parylene C can be produced as uniform films with thicknesses in the submicrometer range by room-temperature chemical vapor deposition. 53,54 Silicon is a typical material in MEMS/NEMS processes due to its toughness and reliability 55 and has a Young's modulus of 169 GPa. 56 In addition, silicon oxide, polysilicon, and silicon nitride can be fabricated more uniformly than polymeric materials.…”

“…In the first method, a flexible membrane is suspended over a substrate that receives irradiation from a laser beam. The deflection of the membrane resulting from the interaction between the target and the bioreceptor is determined by quantifying the shift in the reflected laser beam using either a spectroscope 54 or an interferometer. 63 In the second design, it is possible to integrate a photodetector into the substrate.…”

“…Maeda et al 54 designed a parylene-based MEMS biosensor using a Fabry−Perot interferometer to detect prostate-specific antigen (PSA) (Figure 1a). To construct the proposed biosensor, amino-functionalized parylene C was first coated with PSA−antibodies using glutaraldehyde cross-linking and then suspended as a flexible membrane over a Si substrate with an air gap.…”

Recent Developments in the Field of Optical Immunosensors Focusing on a Label-Free, White Light Reflectance Spectroscopy-Based Immunosensing Platform

“…A micro-sized non-spectroscopic optical reflector gadget was fabricated that was based on anti-analyte antibodies conjugated to retroreflective particles; the gadget was integrated with a commercial smartphone and applied to the detection of the creatine kinase-myocardial band [ 80 ]. Moreover, a Fabry-Pérot interferometric surface stress sensor was developed and applied to detection of prostate-specific antigen (PSA); the sensor employed anti-analyte antibodies covalently immobilized on a deformable biomembrane constructed on a parylene-C nanosheet support/silicon substrate, and the reflection spectra shifts created upon antibody-analyte binding due to membrane deformation were recorded [ 81 ]. Moreover, a planar waveguide immunosensor for zearalenone was described: the waveguide was composed of a thin silicon nitride layer between two thicker silicon dioxide layers, and the sensor worked as a polarization interferometer; the anti-analyte antibody was immobilized on the waveguide via a polyelectrolyte layer on which protein A was adsorbed [ 82 ].…”

“…Several optical immunosensors have been developed for the detection of whole bacteria, such as Staphylococcus aureus [ 68 ], especially methicillin-resistant Staphylococcus aureus [ 54 ], Salmonella typhi VI [ 59 ], Escherichia coli O157 [ 60 ], and Salmonella typhimurium [ 88 ]. Other optical immunosensors have been applied to and/or evaluated for the detection/quantification of specific disease biomarkers, such as neuron-specific enolase [ 56 ], myocardial creatine-kinase [ 80 ], prostate-specific antigen [ 81 ], human epididymis protein 4 [ 57 ], programmed death ligand 1 [ 73 ], cardiac troponin I [ 78 ], and C-reactive protein [ 87 ]. Another group includes optical immunosensors that have been applied to and/or evaluated through the detection/quantification of basic and important biomolecules, such as human INF-γ or insulin [ 62 ], immunoglobulin G [ 69 ], CD5 [ 76 ], collagen I [ 72 ], cortisol [ 74 ], and estrone and estradiol [ 63 ].…”