A distance-based paper sensor for rapid detection of blood lactate concentration using gold nanoparticles synthesized by Satureja hortensis

Abstract Rapid detection of lactate as the major fuel source and material to support the level of blood sugar can open up a new class of analysis for nutritionists and sports medicine practitioners. Here, a rapid and user-friendly method for monitoring changes in the blood lactate concentration is reported, involving the use of a paper strip coated with gold nanoparticles (AuNPs). The aqueous extract of Satureja hortensis is used as the reduction agent in a green synthesis of the AuNPs. Due to the interaction between the NPs and lactate flowing across the paper strip, they change color from red to purple, which can be detected by the naked eye. It is possible to create a distance-based paper sensor, representing these changes as a column of colored bars on the paper substrate whose length has a good linear relationship with the lactate concentration ranged between 1.0 and 30.0 mM. By recording the color changes with a scanner, the sensor response is also obtained using an image analysis method, leading to a linear calibration curve in the lactate concentration range of 0.5–30.0 mM. The resulting detection limits of the lactate measurements are found to be 0.6 and 0.47 using the distance measurement and image analysis methods, respectively. Interestingly, in the presence of interfering species, the sensor is selective for lactate, while also showing good performance in measuring the lactate concentration in the real blood samples.