\begin{table}[!htb]
\centering
\begin{tabular}{|c||c|c|c|c|}\hline
\diagbox[outerrightsep=10pt, innerrightsep = -10pt, width = 7em]{Ara}{IPTG aTc}
&\makebox[2em]{0 0}&\makebox[2em]{0 1}&\makebox[2em]{1 1}
&\makebox[2em]{1 0}\\ \hline\hline
0 & 1 \tikzmark{a} & 0 & 0 & 0 \tikzmark{b} \\ \hline
1 & 1 & 1 & 0 & 1\\ \hline
\end{tabular}
\begin{tikzpicture}[overlay, remember picture, shorten <=-3pt]
%\draw[->] (a.center) to (b.center);
\draw [->, xshift=7ex] ({pic cs:a}) to ({pic cs:b});
%\draw [->] ([yshift=.75pt]{pic cs:a}) -- ({pic cs:c});