Abstract
Sensitive and selective methods for the determination of urea in samples such as dairy products are important for quality control and health applications. Using ammonium ferric citrate as a precursor, Fe/N-codoped carbon dots (CD(FeN)) were prepared by a hydrothermal procedure and characterized in detail. CD(FeN) strongly catalyzes the oxidation of 3,3',5,5'-tetramethylbenzidine (TMB) by H(2)O(2) to turn on an indicator molecular reaction, forming an oxidized tetramethylbenzidine (TMB(ox)) probe with surface-enhanced Raman scattering, resonance Rayleigh scattering, and fluorescence (SERS, RRS, and FL) signals at 1,598 cm(-1), 370 nm, and 405 nm, respectively. The urea aptamer (Apt) can turn off the indicator reaction to reduce the tri-signals, and the addition of urea turns on the indicator reaction to linearly enhance the SERS/RRS/FL intensity. Thus, a novel Apt turn-on tri-mode method was developed for the assay determination of ultra-trace urea with high sensitivity, good selectivity, and accuracy. Trace adenosine triphosphate and estradiol can also be determined by the Apt-CD(FeN) catalytic analytical platform.