Merging microfluidics with luminescence immunoassays for urgent point-of-care diagnostics of COVID-19

Abstract

The Coronavirus disease 2019 (COVID-19) outbreak has urged the establishment of a global-wide rapid diagnostic system. Current widely-used tests for COVID-19 include nucleic acid assays, immunoassays, and radiological imaging. Immunoassays play an irreplaceable role in rapidly diagnosing COVID-19 and monitoring the patients for the assessment of their severity, risks of the immune storm, and prediction of treatment outcomes. Despite of the enormous needs for immunoassays, the widespread use of traditional immunoassay platforms is still limited by high cost and low automation, which are currently not suitable for point-of-care tests (POCTs). Microfluidic chips with the features of low consumption, high throughput, and integration, provide the potential to enable immunoassays for POCTs, especially in remote areas. Meanwhile, luminescence detection can be merged with immunoassays on microfluidic platforms for their good performance in quantification, sensitivity, and specificity. This review introduces both homogenous and heterogenous luminescence immunoassays with various microfluidic platforms. We also summarize the strengths and weaknesses of the categorized methods, highlighting their recent typical progress. Additionally, different microfluidic platforms are described for comparison. The latest advances in combining luminescence immunoassays with microfluidic platforms for POCTs of COVID-19 are further explained with antigens, antibodies, and related cytokines. Finally, challenges and future perspectives were discussed.

Keywords: COVID-19; Luminescence immunoassays; Microfluidic chips; POCTs.

Fig. 1

Schematic illustration of luminescence immunoassays on microfluidic chips. (Reprinted with permission from Refs. [88,333,365]).

Fig. 2

(A) Schematic illustration of the competitive immunoassays on microfluidic chips for CRP detection. (Reprinted with permission from Ref. [116]). (B) Diagram of a test strip transformed into a capillary-driven microfluidic chip. (Reprinted with permission from Ref. [121]). (C) Schematic diagram of AIEgens for dual-modality readout immunoassays. (Reprinted with permission from Ref. [136]). (D) Schematic diagram of the AIE₈₁₀NP-based test strip for IgM, IgG against SARS-CoV-2 detection. (Reprinted with permission from Ref. [137]).

Fig. 3

(A) Schematic diagram of magneto–fluorescent assemblies for ICA. (a) Principle of PCT separation and enrichment. (b) Schematic illustration of the whole workflow of ICA and corresponding results. (Reprinted with permission from Ref. [143]). (B) Schematic diagram of gravity-driven microfluidic siphons for immunoassays with a mobile phone. (Reprinted with permission from Ref. [152]). (C) Schematic diagram of electro-driven ICA integrated with UCNPs. (a) Principle of the electro-driven ICA. (Reprinted with permission from Ref. [153]).

Fig. 4

DCLIAs on microfluidic chips. (A) Schematic illustration of the aptamer-antibody DCLIAs on the integrated microfluidic system. (a) Transfer of the MBs to the transportation unit for reaction. (b) Washing with phosphate buffer. (c) Transfer of acridinium ester-labeled antibodies to the transportation unit for reaction. (d) Washing with phosphate buffer once again. (e) Transfer of H₂O₂ to the transportation unit. (f) Transfer of the complexes to the NaOH chamber for chemiluminescence immunoassays. (Reprinted with permission from Ref. [174]). (B) Schematic illustration of three heart disease biomarkers by magnetic carbon composites and the three-dimensional microfluidic paper-based device. (Reprinted with permission from Ref. [177]). (C) Schematic diagram of novel long-lasting chemiluminescence system. (Reprinted with permission from Ref. [178]).

Fig. 5

(A) Workflow of active droplet-array microfluidics-based ICLIAs. (Reprinted with permission from Ref. [194]). (B) Schematic illustration of the on-chip valve-assisted microfluidic chip for multiple biomarkers with dynamic detection ranges. (Reprinted with permission from Ref. [188]).

Fig. 6

(A) Schematic illustration of the flux-adaptable and pump-free microfluidic system. (Reprinted with permission from Ref. [189]). (B) Schematic illustration of the 3D-printed microfluidic chip with online cell lysis for biomarkers detection at single-cell levels. (Reprinted with permission from Ref. [190]).

Fig. 7

ECLIAs on microfluidic chips. (A) Schematic illustration of the paper-based ECL biosensing platform. (a) Procedure of immunoassay in tubes. (b) Fabrication of paper-based screen-printed electrodes and matched detection device. (Reprinted with permission from Ref. [200]). (B) Schematic illustration of the rotational paper-based analytical device. (a) Step by step immunoassays controlled by the rotational valves. (b) The whole workflow of ECLIAs on the device (Reprinted with permission from Ref. [201]).

Fig. 8

LRET immunoassays on microfluidic chips. (A) Schematic illustration of BRET immunoassays on the microfluidic thread-based analytical devices with a mobile phone. (Reprinted with permission from Ref. [228]). (B) The on-chip immunophenotyping immunoassays by AlphaLISA. (Reprinted with permission from Ref. [234]).

Fig. 9

Digital immunoassays on microfluidic chips. (A) Schematic illustration of multiplexed digital immunoassays on the microstructured microfluidic chip. (Reprinted with permission from Ref. [248]). (B) Design of the microdroplet Megascale Detector system. (a) The top view and bottom view of the chip. (b) Photograph of the chip. (c) Micrograph of the droplet generator encapsulate microbeads into droplets. (d) Fluorescence micrograph of the droplets. (e) Diagram of the system, including the microdroplet Megascale Detector chip and a mobile phone, and three light sources. (Reprinted with permission from Ref. [240]).

Fig. 10

Integrated microfluidic platforms. (A) Schematic illustration of the gravity-driven chip. (Reprinted with permission from Ref. [278]). (B) Photograph and schematic illustration of the fabricated LOAD. (Reprinted with permission from Ref. [296]). (C) Images of Scheme of the chemiluminescent LFIAs for the detection of targets. (Reprinted with permission from Ref. [312]). (D) Schematic diagrams of the μPADs design and the direct ELISA protocol. (Reprinted with permission from Ref. [318]).

Fig. 11

Luminescence immunoassays for COVID-19 antigen or antibody tests. (A) Schematic illustration of the LumiraDx SARS-CoV-2 antigen assay. (a) Principle of the sandwich immunoassays. (b) Image of the LumiraDx system. (c) Image of instrument result screen. (Reprinted with permission from Ref. [333]). (B) Schematic illustration of DA-D4 POCT and analytical validation. (a) Principle of the sandwich immunoassays on the DA-D4. (b) Images of open format DA-D4. (c) Images of microfluidic DA-D4. (d) D4Scope and cut-away view of the optical path. (e) Analytical validation of the open-format DA-D4. (f) Analytical validation of microfluidic DA-D4. (g) Representative D4 detection spots. (Reprinted with permission from Ref. [343]).

Fig. 12

Luminescence immunoassays for COVID-19 antigen and antibody tests. (A) Schematic illustration of the p-BNC platform for COVID-19 diagnostics. (a) The p-BNC platform with 20 spatially programmable bead sensors for (b) biomarkers and (c) antibodies detection. (Reprinted with permission from Ref. [363]). (B) Schematic illustration of the centrifugal microfluidic immunoassays for IgG, IgM, and antigen detection of SARS-CoV-2. (Reprinted with permission from Ref. [364]). (C) Schematic illustration of Simoa for neutralization assays against SARS-CoV-2. (Reprinted with permission from Ref. [372]).