  We explore the closed form of the correlation function of four spin operators
(including one closed string Ramond-Ramond (RR) and two open string fermions)
and one current in ten dimensions, to be able to find the complete and the
closed form of the amplitude of one closed string Ramond-Ramond, one gauge
field and two fermionic strings (with the same chirality) to all orders in
$\alpha'$ in IIB superstring theory. In particular we use a special gauge
fixing to the amplitude and apply fermions' equations of motion to $<V_{C}
V_{A}V_{\bar\psi}V_{\psi} >$ correlator. String amplitude induced that neither
there should be any $u-$channel gauge poles for $p=n+2$ case nor there are
couplings between two fermions and two gauge fields for $p=n$ case in the field
theory of type IIB. All infinite $u-$ channel scalar poles and $t,s-$channel
fermion poles of the string amplitude are useful in discovering new couplings
of type IIB. More specifically, by making use of the SYM couplings of one
scalar, one gauge and two fermions and their all order $\alpha'$ higher
derivative corrections, we are able to exactly produce all infinite $(s+t+u)-$
channel scalar poles of $<V_{C} V_{A}V_{\bar\psi}V_{\psi} >$ .
