A study on the combination of enzyme stabilizers and low temperature in the long-term storage of glutamate biosensor

The importance of physiological glutamate has been widely demonstrated in cognitive and memory processes but also in neurotransmission. Its involvement in several pathologies has been established as well. Therefore, to have available analytical devices allowing the study of its variations becomes of fundamental importance, in particular in preclinical studies. Often the necessary know-how to develop and characterize biosensors for the glutamate detection is restricted to a few research groups while much more numerous are those who would like to implant such analytical devices to study the glutamatergic system in vivo. On theses basis, a series of studies have been undertaken aimed at the middle-time storage of biosensors, so that their use results being independent from the construction and characterization process in order to allow their wider diffusion and use. Therefore, it results very important to find the best storage conditions in order to extend the life and functionality of the biosensors, especially due to the over-time instability of the enzyme present on the surface. In the present study, it has been studied the impact of glycols, such as glycerol and triethylene glycol, as enzyme stabilizer coupled with the long-term storage at low temperatures (-20°C and -80°C) on the biosensors’ performances. Biosensors were observed for 5 months and evaluated in terms of enzymatic activity by measuring VMAX and KM. Evaluations on the analytical features were made as well, in terms of Linear Region Slope, which represents one the most important parameter indicating the efficiency and the sensitivity of the biosensor. Interestingly, both glycols proved capable of increasing the enzymatic activity and maintaining a good efficiency of the biosensors over time. Moreover, the combination with low-temperature storage pointed out a different behavior of the two glycols. In particular, glycerol proved to be more effective in stabilizing the enzyme and maintaining analytical performance when the biosensors were stored at -20°C. Instead, triethylene glycol proved to perform the same function of the glycerol but when the biosensors were stored at -80°C.