  In this paper we consider a class of partial integro-differential equations
of fractional order, motivated by an equation which arises as a result of
modeling surface-volume reactions in optical biosensors. We solve these
equations by employing techniques from fractional calculus; several examples
are discussed. Furthermore, for the first time, we encounter an order of the
fractional derivative other than $\frac{1}{2}$ in an applied problem. Hence, in
this paper we explore the applicability of fractional calculus in real-world
applications, further strengthening the true nature of fractional calculus.
