Opto-Microfluidic Immunosensors: From Colorimetric to Plasmonic

Abstract

Optical detection has long been the most popular technique in immunosensing. Recent developments in the synthesis of luminescent probes and the fabrication of novel nanostructures enable more sensitive and efficient optical detection, which can be miniaturized and integrated with microfluidics to realize compact lab-on-a-chip immunosensors. These immunosensors are portable, economical and automated, but their sensitivity is not compromised. This review focuses on the incorporation and implementation of optical detection and microfluidics in immunosensors; it introduces the working principles of each optical detection technique and how it can be exploited in immunosensing. The recent progress in various opto-microfluidic immunosensor designs is described. Instead of being comprehensive to include all opto-microfluidic platforms, the report centers on the designs that are promising for point-of-care immunosensing diagnostics, in which ease of use, stability and cost-effective fabrication are emphasized.

Keywords: immunosensing; microfluidics; optical detection.

Figure 1

Comparison of immunosensing with optical probes. (A) Colorimetric and chemiluminescence (CL) induced by an enzyme; (B) Colorimetric changes by light absorption and scattering of a nanoparticle; (C) Electrochemiluminescence (ECL) from an electrochemically excited probe; (D) Photoluminescence from an optically excited probe.

Figure 2

Mechanisms of luminescence. (A) Absorption of electromagnetic radiation, photoluminescence and chemiluminescence; (B) chemiluminescence; (C) electrochemiluminescence. Figure 2B is reproduced with permission from the Chemical Connection website [63].

Figure 3

A prism-based SPR sensor with a gold film as sensing layer. The light is absorbed by surface plasmons at a particular resonant angle.

Figure 4

A 96-microzone paper-based ELISA [92]. Reproduction of the figures is made with permission of Wiley.

Figure 5

Paper-based microfluidics [94]. (A) A 3D paper-based immunosensor using an origami method: 1. Photolithographically patterned channels on chromatography paper; 2. Top layer of the device; 3. Bottom layer of the device; 4. Aluminium housing; 5. Colored solutions were injected into designated channels. (B) Photoluminescent detection on the paper surface. Reproduction of the figures is made with permission of American Chemical Society.

Figure 6

DMF further integrated another platform to perform immunoassays as described in: (A–C) Rackus et al. [36]; (D,E) Zeng et al. [62]. (A) DMF device with integrated nanostructured microelectrodes; (B) Schematic of a cross section of a DMF device; (C) Electrochemical measurements of the DMF device; (D) Schematic of the DMF chemiluminescent detector; (E) Mixing process on the DMF device (1–5); chemiluminescent photo (6) and schematic diagram (7). Reproduction of the figures is made with permission of Royal Society of Chemistry.