The synthesis and biomedical applications of nano/micromotors have attracted great attention. In this work, preparation and characterization of catalytic gold/poly(3,4-ethylenedioxythiophene)/platinum (Au/PEDOT/Pt) micromotors were reported to present their contribution for cancer biomarker miRNA-21 detection. Potential use of these motors for possible cancer treatment was also illustrated after their biocompability had shown. At first, anti-miRNA probe immobilized Au/PEDOT/Pt micromotors (probe DNA/Au/PEDOT/Pt/MMs) were used for the sensitive and selective recognition of synthetic miRNA-21 target sequence to present the proof-of-concept. Then intracellular studies were carried out using four types of cancer cells (human breast cancer cell line, MCF-7, human colorectal adenocarcinoma cell line, HT-29, human lung carcinoma cell line, A-549 and human osteosarcoma cell line, SJSA-1). These studies illustrated the high selectivity of probe DNA/Au/PEDOT/Pt micromotors for MCF-7 and SJSA-1 cells. Later, antiproliferative and cytotoxic effects of the micromotors and their potential use for breast cancer treatment were investigated.