Article
Advantages of Highly Spherical Gold Nanoparticles
as Labels for Lateral Flow Immunoassay
Nadezhda A. Byzova
1
, Anatoly V. Zherdev
1
, Boris N. Khlebtsov
2,
*, Andrey M. Burov
2
,
Nikolai G. Khlebtsov
2,3
and Boris B. Dzantiev
1,
*
1
A.N. Bach Institute of Biochemistry, Research Center of Biotechnology, Russian Academy of Sciences,
Moscow 119071, Russia; nbyzova@mail.ru (N.A.B.); zherdev@inbi.ras.ru (A.V.Z.)
2
Institute of Biochemistry and Physiology of Plants and Microorganisms, Russian Academy of Sciences,
Saratov 410049, Russia; burov_a@ibppm.ru (A.M.B.); khlebtsov_n@ibppm.ru (N.G.K.)
3
Saratov State University, Saratov 410012, Russia
* Correspondence: khlebtsov_b@ibppm.ru (B.N.K.); dzantiev@inbi.ras.ru (B.B.D.);
Tel.: +7-8452-97-0403 (B.N.K.); +7-495-954-3142 (B.B.D.)
Received: 15 May 2020; Accepted: 23 June 2020; Published: 26 June 2020
Abstract:
The use of lateral flow immunoassays (LFIAs) for rapid on-site testing is restricted by their
relatively high limit of detection (LoD). One possible way to decrease the LoD is to optimize nanoparticle
properties that are used as labels. We compare two types of Au nanoparticles: usual quasispherical
gold nanoparticles (C-GNPs), obtained by the Turkevich–Frens method, and superspherical gold
nanoparticles (S-GNPs), obtained by a progressive overgrowth technique. Average diameters were
18.6–47.5 nm for C-GNPs and 20.2–90.4 nm for S-GNPs. Cardiomarker troponin I was considered as
the target analyte. Adsorption and covalent conjugation with antibodies were tested for both GNP
types. For C-GNPs, the minimal LoD was obtained with 33.7 nm nanoparticles, reaching 12.7 ng/mL for
covalent immobilization and 9.9 ng/mL for adsorption. The average diameter of S-GNPs varied from
20.2 to 64.5 nm, which resulted in a decrease in LoD for an LFIA of troponin I from 3.4 to 1.2 ng/mL
for covalent immobilization and from 2.9 to 2.0 ng/mL for adsorption. Thus, we obtained an 8-fold
decrease in LoD (9.9 to 1.2 ng/mL) by using S-GNPs. This effect can be related to more effective antibody
immobilization and improved S-GNP optical properties. The obtained results can improve LFIAs for
various practically significant analytes.
Keywords:
immunochromatography; nanosized labels; nanoparticle–antibody conjugates;
assay sensitivity; cardiomarker
1. Introduction
Lateral flow immunoassay (LFIA)—also known as immunochromatography—has been
suggested as an effective analytical method for point-of-care diagnostics [
1
,
2
]. The design of the
immunochromatographic test strip with pre-applied reagents ensures the autonomous implementation
of all analytical processes. The assay can be initiated by a simple contact of the test strip with the sample
and does not require additional manipulations with reagents and devices. A quick immunospecific
reaction (5–15 min) leads to the formation of visually detectable stained zones in certain areas of
the test strip with nanoparticle-labeled immune complexes [
3
,
4
]. However, the fast reaction kinetics
and absence of the additional signal amplification step lead to the relatively low sensitivity of LFIA
compared to other types of immunoassay.
Various approaches have been considered for increasing LFIA sensitivity, including multistep
analysis and specific detection techniques [
5
–
7
]. However, such improvements result in the loss of
the main advantage of LFIA as a simple point-of-care test. A promising approach is to optimize
Sensors 2020, 20, 3608; doi:10.3390/s20123608 www.mdpi.com/journal/sensors
