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Among various nanobiosensor, it has a lot of advantage when usingrare-earth nanoparticles as probe, such as larger stokes shifts, narrowemission profiles, long fluorescence lifetime, and low toxicity. At the sametime, because of the special anti-stokes luminous phenomenon, upconversionrare-earth nanoparticles （UCNPs） show very low background fluorescence,minimal photo damage and deep penetration in the analysis of biological andmedicinal application. Combine with the virtue of biosensor （specificity anddiversity of biological reaction）, we synthesized rare-earth-based fluorescentmaterials CePO4:Tb3+3+, NaYF4:Yb,Er3+and NaYF+4:Yb3,Tm3+UCNPs，andmodified UCNPs with different aptamers, then established novel methods fordetermination of biological substances based on FRET. The details aresummarized as follows:（1） By using facile solvothermal technology, CePO4:Tb3+nanocrystalswere prepared using nitrate and phosphate as raw materials. A fluorescenceresonance energy transfer （FRET） system between CePO4:Tb3+nanocrystalsas donor and Co2+ions as acceptor was built. Based on the fluorescencequenching of CePO4:Tb3+nanocrystals in the presence of Co2+ions, a simpleand sensitive method was developed for the determination of trace amountsof Co2+ions in aqueous solutions. Under the optimum conditions, the linear range and the detection limit for Co2+ions are5nM-1.8μM and3.5nM,respectively. The method was applied successfully to the determination ofCo2+ions in water samples with satisfactory results.（2） In the study, we successfully synthesized NaYF4:Yb3+,Er3+andNaYF+4:Yb3+,Tm3UCNPs by hydrothermal/solvothermal method. Byemploying them as donor and Au NRs with different maximum absorptionwavelengths as acceptor, two efficient FRET systems were built. Aftermodifying thrombin aptamers, the two FRET systems were subsequentlydemonstrated for the determination of thrombin in aqueous solutions andblood samples. Under the optimum conditions, the linear ranges in aqueoussolutions are2.5-90nM and0.375-11.25nM, respectively. The detection limitof thrombin is1.5nM and0.118nM, respectively.（3） A FRET system between NaYF+4:Yb3,Tm3+UCNPs and Au NRs with ahigh absorption band around808nm was established. Then the two probeswere conjugated with the Hg2+aptamer. Therefore, a selective method forHg2+ions detection was developed. Under the optimum conditions, the linearrange and the detection limit for Hg2+ions are5-100nM and2nM,respectively. The method was applied successfully to the determination ofHg2+ions in water and human serum samples with satisfactory results.
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