<p>Contamination of surface water and drinking water with pharmaceuticals presents an environmental concern. It has been shown to affect aquatic organisms and have adverse health effects on humans. One of the most common pharmaceutical contaminants is the opioid analgesic tramadol. In this communication, we report on the first surface plasmon resonance biosensor-based detection of tramadol in water. The biosensor utilizes a binding inhibition format and enables detection of tramadol at a wide range of concentrations (5 orders of magnitude) with a limit of detection of 0.52 µg/L. The results of a small-scale environmental study are reported in which the biosensor was used to analyze river water samples. The results were found to agree well with those obtained using the liquid chromatography-tandem mass spectrometry (HPLC–MS/MS).</p> Graphical abstract <p></p>