Retracted Article: Study and development of an optical waveguide cap for biomedical application Margarida Ferreira, Catarina S. Monteiro, Patrícia C. Henriques, Inês C. Gonçalves and Orlando Frazão EPJ Web Conf., 266 (2022) 13011 Published online: 13 October 2022 DOI: 10.1051/epjconf/202226613011