Estimation of Extracellular Matrix Production Using a Cultured-Chondrocyte-Based Gate Ion-Sensitive Field-Effect Transistor

Autologous chondrocytes are generally evaluated by mechanical, histological, and biochemical methods. However, the analyzed data are from discontinuous measurements at an end point, during which living chondrocytes are destroyed and stained. To solve the problem, we developed a label-free and noninvasive method of estimating extracellular matrix (ECM) production that results from chondrocyte metabolic activities using a cultured-chondrocyte-based gate ion-sensitive field-effect transistor (ISFET) in this study. Using the cultured-chondrocyte-based gate ISFET sensor, we found that the change in electrical signal (ΔV_out), which indicated the change in interfacial pH at the chondrocyte/gate nanogap (ΔpH_int), gradually increased over 3 weeks upon adding a biologically active substance, l-ascorbic acid phosphate magnesium salt n-hydrate (APM), which was attributable to chondrocyte metabolic activities. The increase in ΔV_out (ΔpH_int) caused by the chondrocyte metabolic activities was also confirmed by the observation of the suppression of chondrocyte metabolism upon adding 2-deoxy-d-glucose, which was clearly monitored using the cultured-chondrocyte-based gate ISFET sensor. In particular, ΔV_out increased monotonically with increasing APM concentrations, indicating that the addition of APM increased ΔV_out (ΔpH_int), the amount of which depended on the APM concentration. Moreover, the amounts of hydroxyproline and sulfated glycosaminoglycan (sGAG) as the main components of ECM, which were quantified by colorimetry using various APM concentrations, were found to have a linear relationship with ΔV_out (ΔpH_int) of the cultured-chondrocyte-based gate ISFET sensor. Therefore, a platform based on the cultured-chondrocyte-based gate ISFET is suitable for a label-free, noninvasive, and real-time measurement system to analyze ECM production by autologous chondrocytes before transplantation.