Thulium- and Erbium-Doped Nanoparticles with Poly(acrylic acid) Coating for Upconversion Cross-Correlation Spectroscopy-based Sandwich Immunoassays in Plasma

: Lahtinen Satu, Liisberg Mikkel Baldtzer, Raiko Kirsti, Krause Stefan, Soukka Tero, Vosch Tom

Publisher: American Chemical Society

: 2021

ACS Applied Nano Materials

: ACS APPLIED NANO MATERIALS

: ACS APPL NANO MATER

: 4

: 1

: 432

: 440

: 9

: 2574-0970

DOI: https://doi.org/10.1021/acsanm.0c02770

Fluorescence correlation spectroscopy based on upconverting nano-particles (UCNPs) can detect single particles in strongly autofluorescent samples, such as plasma. Nanoparticle aggregation, however, is a problem in correlation spectroscopy measurements, and biological media are known to induce aggregation. Here we present an improved UCNP surface chemistry and use these UCNPs in an upconversion cross-correlation spectroscopy (UCCS)-based homogeneous immunoassay for thyroid-stimulating hormone, where the simultaneous emission of green- (NaYF4 :Yb3+,Er3+ ) and blue- (NaYF4 :Yb3+,Tm3+) emitting UCNPs is detected when they are bound together by the analyte. The improved coating suppresses UCNP aggregation, even in plasma samples. Additionally, increasing the Tm doping of blue-emitting UCNPs enhances their brightness at a high excitation intensity and also results in a significantly shorter luminescence decay time, which improves the probability of detecting coincident blue and green emission from the bound UCNPs in the UCCS immunoassay.

correlation spectroscopy, high lanthanide doping, reduced aggregation, single-molecule detection, Thyroid stimulating hormone