Improvement of sensitivity of the light-addressable potentiometric sensors for the purpose of noninvasive measurement of electrical activity of biological cells

The possibility of measurement of the electrical activity of neurons by Light-Addressable Potentiometric Sensor (LAPS) is investigated in this article. For the measurement of the extracellular transient of the neural action potential, which is very low, at the surface of a LAPS heterostructure, a simple structure like SiO₂/Si, instead of the conventional Si₃N₄/SiO₂/Si heterostructure, is studied. The SiO₂ surface was modified by Poly-L-Ornithine and Laminin (PLOL). Experimental results show that the PLOL coating on the SiO₂ surface not only prevents the hydration of the SiO₂ layer and thus enables us to use SiO₂ only as the insulating layer, but also, provides an efficient culturing of neurons of Lymnaea stagnalis, a kind of sea snail, on the SiO₂ surface. The PLOL modified SiO₂ layer of the novel LAPS heterostructure, is kept in contact with the neuron-culture medium for ten days mimicking the maximum cell-culturing period. There is no appreciable change in the sensor response was observed during this period. A DC bias, superimposed by a 2 mV_p-p and 800 Hz AC was applied to the sensor to simulate an extracellular transient of 2 mV_p-p to the surface and the response of the sensor shows the possibility of the measurement of the neural action potential by the LAPS.