Preparation and application of silver nanoparticle capped carbon dots composite as fluorescent probe for cobalt determination in vitamin B12 supplement samples

Abstract

A simple and economical material of fluorescence nanocomposite was developed to quantify vitamin B12 through cobalt(II) ion measurement. The material was derived from carbon dots capped with silver nanoparticles, forming spherical AgNPs@CDs composite with the average diameter of 8.7 nm, expressing unique optical properties, and was used as an optical probe for Co(II) ion determination. The synthesized AgNPs@CDs showed a maximum absorption peak at the wavelength of 406 nm, while their fluorescence peak appeared at the wavelength of 526 nm under the excitation wavelength of 406 nm. The nanocomposites exhibited stable fluorescence with IC50 value against human cholangiocyte cell line of 137.7 ppm after 24 h of the treatment. The interaction between Co(II) ions and AgNPs@CDs effervesced molecular oxygen and caused fluorescence quenching of the composite material. The optimum conditions for Co(II) ion detection were pH 10, volume ratio between AgNPs@CDs and Co(II) ion of 0.10:0.90, and reaction time of 30 min. The linearity range based on the Stern–Volmer plot was 0.05–10.00 ppm, and the limit of detection and limit of quantification were 0.032 ppm and 0.095 ppm, respectively. The developed approach was used to determine the extracted Co(II) ions in commercial vitamin B12 supplement samples and their spiked extracts. The results showed good agreement with those from a conventional method of atomic emission spectrometry, and acceptable range of recovery from 90.0 to 105.0 % was obtained. The fluorescence quenching mechanism of the AgNPs@CDs was elucidated based on the characterization information from several analytical techniques, and electrocatalytic reaction between the nanocomposite and Co(II) species was proposed.