Homogeneous Assay for Whole Blood Folate Using Photon Upconversion

Abstract

Red blood cell folate is measured for folate deficiency diagnosis, because it reflects the long-term folate level in tissues, whereas serum folate only represents the dietary intake. Direct homogeneous assay from whole blood would be ideal but conventional fluorescence techniques in blood suffer from high background and strong absorption of light at ultraviolet and visible wavelengths. In this study, a new photon upconversion-based homogeneous assay for whole blood folate is introduced based on resonance energy transfer from upconverting nanophosphor donor coated with folate binding protein to a near-infrared fluorescent acceptor dye conjugated to folate analogue. The sensitized acceptor emission is measured at 740 nm upon 980 nm excitation. Thus, optically transparent wavelengths are utilized for both donor excitation and sensitized acceptor emission to minimize the sample absorption, and anti-Stokes detection completely eliminates the Stokes-shifted autofluorescence. The IC50 value of the assay was 6.0 nM and the limit of detection (LOD) was 1 nM. The measurable concentration range was 2 orders of magnitude between 1.0-100 nM, corresponding to 40-4000 nM folate in the whole blood sample. Recoveries of added folic acid were 112%-114%. A good correlation was found when compared to a competitive heterogeneous assay based on the DELFIA-technology. The introduced assay provides a simple and fast method for whole blood folate measurement.

Impact of Lanthanide Nanomaterials on Photonic Devices and Smart Applications

“…Autofluorescence is avoided because of the anti‐Stokes measurement. Reproduced with permission . Copyright 2014, American Chemical Society.…”

Synthesis of Luminescent Carbon Dots with Ultrahigh Quantum Yield and Inherent Folate Receptor-Positive Cancer Cell Targetability

“…Folic acid (FA), one of the B vitamins, is an essential dietary component that can effectively decrease the risk of several diseases 21 , 22 , such as neural-tube defects and congenital heart defects. Particularly, FA has a good targetability to cancer cells 23 , 24 .…”

Effective Shielding of NaYF4:Yb3+,Er3+ Upconverting Nanoparticles in Aqueous Environments Using Layer-by-Layer Assembly

“…Materials exhibiting upconversion luminescence 1 have been studied intensively for the last decade because of their potential use in photovoltaics, 2 , 3 biomedical imaging and theranostics, 4 − 6 and in biomedical assays. 7 − 9 Especially, the research in the biomedical field has benefitted from the extensive development of upconversion material syntheses, resulting in nanoscale materials down to 5 nm. 10 − 13 Currently, hexagonal β-NaYF 4 :Yb 3+ ,Er 3+ is considered to be the most efficient material in upconversion.…”