New upper bounds for Estrada index of bipartite graphs

Suppose G is a graph and λ1,λ2,…,λn are the eigenvalues of G. The Estrada index EE(G) of G is defined as the sum of eλi, 1≤i≤n. In this paper some new upper bounds for the Estrada index of bipartite graphs are presented. We apply our result on a (4,6)-fullerene to improve our bound given in an earlier paper.