Fabrication, Analysis, Simulation, and Application of the Nanohole Array Sensor



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Nanohole arrays in metal films have many amazing optical properties based on the surface plasmon resonance, which makes it popular in the sensing field. Usually, the change of the refractive index on the metal surface of nanohole arrays, caused by the binding of an analyte, can be reflected on the peak shift or intensity change of the transmission or reflection spectra. As sensing components, nanohole arrays provide many important advantages, including high reproducibility, miniaturization, the ability to integrate with other techniques, the capability of high-throughput analysis, and so on. Nanohole array sensing is quite compatible with the lab-on-chip technology and meets the tendency of point-of-care diagnostics that have been dramatically developed in recent years. Point-of-care diagnostics require low cost and portable devices with reliable and robust sensitivity for special analytes such as viruses. With the help of the nanohole arrays, the individual molecule of nanoscale size can be directly and precisely located. In this work, we have fabricated nanohole arrays with 150 nm diameter and 2 μm period, which have a larger period than those reported by other papers. Silica-shelled gold nanospheres with 70 nm core diameter and 20 nm shell thickness are used to block the nanoholes; and darkfield imaging system is used to obtain the images by the CCD and spectra by the spectrometer. The images and spectra of the nanoholes blocked by the individual nanospheres are analyzed and compared with those of the nanoholes before blocking. Results show a significant reduction of the light intensity in the blue and green light regions but an unusual enhancement in the red light region. FDTD simulations are also conducted to not only confirm the experimental results but also provide the information about the position and the size of the nanospheres inside the nanoholes, and the wavelength of the exciting light. Furthermore, we demonstrate that our nanohole array samples can be integrated into a home-made inexpensive darkfield microscope and analyzed by a smartphone with an application developed by ourselves, which make it viable for future POC diagnostics.



Nanohole array sensor