<p>We present a novel Se(IV)-mediated etching protocol to control the etching orientation and geometrical evolution of bare gold nanorods (AuNRs) and exploit it as a highly sensitive surface-enhanced electrochemiluminescence (ECL) sensor. The initial etching orientation was intimately governed by the concentrations of Se(IV) and cetyltrimethylammoniumbromide&#xa0;(CTAB). Interestingly, an extraordinary lateral etching was preferentially observed in the Se(IV)/KI/CTAB system, leading to the formation of quasi-rectangular AuNRs with increased aspect ratio. This etching process afforded clear geometrical transformation, enabling the efficient synthesis of cubic gold nanoparticles and quasi-rectangular nanorods with an enhanced electric-field enhancement factor. The etched AuNRs immobilized on a glassy-carbon electrode produced a markedly enhanced ECL signal 4.42-fold higher than that of the unetched AuNRs. A detection limit as low as 9.24 pM was achieved for the p53 biomarker carrying a codon-249 mutation. Moreover, the method yielded a lower selectivity factor than previously reported strategies, highlighting its high selectivity and potential for discriminating mutant p53 DNA. Our study significantly advanced current p53 sensor capabilities and highlighted the power of etched plasmonic metasurfaces for sensitive optical detection.</p> Graphical abstract <p></p>