Abstract
The use of a robust optical signaling probe with a high signal-to-noise ratio is important in the development of immunoassays. Lanthanide chelates are a promising material for this purpose, which provide time-resolved luminescence (TRL) due to their large Stokes shift and long luminescence lifetime. From this, they have attracted considerable interest in the in vitro diagnostics field. However, the direct use of lanthanide chelates is limited because their luminescent signal can be easily affected by various quenchers. To overcome this drawback, strategies that rely on the entrapment of lanthanide chelates inside nanoparticles, thereby enabling the protection of the lanthanide chelate from water, have been reported. However, the poor stability of the lanthanide-entrapped nanoparticles results in a significant fluctuation in TRL signal intensity, and this still remains a challenging issue. To address this, we have developed a Lanthanide chelate-Encapsulated Silica Nano Particle (LESNP) as a new immunosensing probe. In this approach, the lanthanide chelate is covalently crosslinked within the silane monomer during the silica nanoparticle formation. The resulting LESNP is physically stable and retains TRL properties of the parent lanthanide chelate. Using the probe, a highly sensitive, sandwich-based TRL immunoassay for the cardiac troponin I was conducted, exhibiting a limit of detection of 48 pg/mL. On the basis of the features of the LESNP such as TRL signaling capability, stability, and the ease of biofunctionalization, we expect that the LESNP can be widely applied in the development of TRL-based immunosensing.
Highlights
The sensitive and accurate immunoassay of disease markers in biological specimens from patients is a cornerstone in in vitro diagnostics (IVD) [1,2,3]
To develop luminescent nanoparticular probes exhibiting robust lanthanide-based time-resolved luminescence (TRL) property, the lanthanide luminophore chelates should be encapsulated inside a solid particle to separate and protect the luminophore chelates from water molecules, which significantly reduce the luminescent signal by quenching [35]
We focused on the development of a nanoparticle synthetic protocol that allowed for the covalent conjugation of a lanthanide luminophore inside of a silica nanoparticle [56,57]
Summary
The sensitive and accurate immunoassay of disease markers in biological specimens from patients is a cornerstone in in vitro diagnostics (IVD) [1,2,3]. Early-stage analysis in disease is important because it can help clinicians make appropriate clinical decisions to allow for prompt and effective treatment From this point of view, the development of immunosensing technologies that provide high sensitivity and accuracy is regarded as the most significant issue in Biosensors 2017, 7, 48; doi:10.3390/bios7040048 www.mdpi.com/journal/biosensors. The sensitivity of any immunosensors is closely related to the type of signal reporter employed and its corresponding signaling capability [8,9,10] In this regard, there have been numerous studies aimed at the development of materials that could be used as effective immunosensing probes [11,12,13,14]. The use of conventional fluorophores in an immuno-analysis that requires high sensitivity, such as the detection of cardiac troponin I (cTnI)
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