Carbon dots as a fluorescent probe for label-free detection of physiological potassium level in human serum and red blood cells

• A unique photoluminescence carbon dots with larger size were prepared by microwave-assisted method.
• A highly sensitive CD-based fluorescence probe for label-free detection of K+ was established.
• Physiological potassium levels of human serum and red blood cells may be directly and rapidly detected.

A unique photoluminescence carbon dots (CDs) with larger size were prepared by microwave-assisted method. Complex functional groups on the surface of the CDs facilitate the nanoparticles to form affinity with some metal ions. Taking advantage of the effective fluorescence quenching effect of K+, a highly sensitive CD-based fluorescence analytical system for label-free detection of K+ with limit of detection (LOD) 1.0 × 10−12 M was established. The concentrations of potassium ion in biological samples such as human serum are usually found at millimolar levels or even higher. The proposed method begins with a substantial dilution of the sample to place the K+ concentration in the dynamic range for quantification, which covers 3 orders of magnitude. This offers some advantages: the detection of K+ only needs very small quantities of biological samples, and the dilution of samples such as serum may effectively eliminate the potential interferences that often originate from the background matrix. The determined potassium levels were satisfactory and closely comparable with the results given by the hospital, indicating that this fluorescent probe is applicable to detection of physiological potassium level with high accuracy. Compared with other relative biosensors requiring modified design, bio-molecular modification or/and sophisticated instruments, this CD-based sensor is very simple, cost-effective and easy detection, suggesting great potential applications for successively monitoring physiological potassium level and the change in biological system.

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