THE INFLUENCE OF OPTICAL GLASS AS A SUBSTRATE IN SPR SENSORS ON THE TEMPERATURE STABILITY OF MEASUREMENT RESULTS

Abstract

The influence of the properties of the substrate made from optical glass of surface plasmon resonance (SPR) sensors on the temperature stability of measurements at a temperature change from 20 to 30°C, in which research is most often carried out, was studied. The phenomenon of surface plasmon resonance is very sensitive to any changes at the metal-dielectric interface, so studying the influence of the temperature factor is an actual task. Research in the infrared region of the spectrum is important because in this case the possible thickness of the research object increases, and it is also possible to reduce the thickness of the gold layer that is sprayed to the glass substrate of the sensory element from 50 nm to 30 nm. But heating the sensitive element with an IR laser can introduce an additional error into the measurement results. The sensitive element of the SPR device consists of a plate made of optical glass and a thin layer of gold deposited on it. It is known that materials expand when heated. The difference in temperature coefficients of linear expansion of glass and gold applied to it can lead to unequal expansion of glass (74x10 -7 ) and gold (14.2x10 -6 ), respectively, causing elastic stresses in the gold sensitive layer of the sensor. Sensory elements with a 30 nm gold layer are used for the IR range of measurements, and 50 nm for the visible range. Therefore, we investigated the stability of the results of measuring the angle of surface plasmon resonance minimum at a wavelength of 650 nm (Plasmon-6 device). It was determined that the optical glass of the substrate affects the stability of measurements of the SPR index of air from temperature fluctuations. The period of stabilization of measurement results in the visible range when the temperature changes from 20 to 30 °C to the change in the angle of the SPR minimum changes from 0.0006 degrees/min for Zerodur to 0.0032 degrees/min for flints, i.e. almost 5 times with the thickness of the gold nanolayer 50 nm, and for a thickness of 30 nm it varies from 0.0010 deg/min for crowns and quartz to 0.0013 deg/min for flints. The lowest value corresponds to Zerodur substrates with practically zero temperature coefficient of linear expansion and quartz in this temperature range. To ensure the stability of the results of measurements of SPR characteristics against temperature fluctuations in the range of 20-30°С, it is recommended to use Zerodur, quartz and crowns for the substrates of SPR sensors