A novel hollow rectangular-cored photonic crystal fiber (PCF) has been introduced in this manuscript to numerically investigate various optical properties for sensing five crucial variants of Amino acids. The proficiency of this sensor in detecting these amino acid variants is assessed with the employment of the full-vector finite element method. This anticipated model comprises rectangular air holes only, which assures the fabrication possibilities with the existing fabrication methodologies. The performance metrics are examined in the present time’s most popular operating range Terahertz (THz) regime (in our case it is between 1.5 and 3.5 THz). Our proposed PCF structure attains a significantly higher sensitivity of 99.18% at 3.3 THz. Besides, this sensor also exhibits very negligible EML and confinement losses simultaneously. These encouraging findings guarantee that the proposed PCF sensor may be used in more general application domains such as biosensing, the pharmaceutical and chemical industries, defense control, food safety, etc.