electrode and change the drain current value. The change in the drain current value acts

as the detection mechanism of the LOC devices. The FET-based LOC devices have ad­

vantages such as being small in size, suitable for mass production, and low cost.

5.3 Nanomaterials and Lab-on-a-Chip Technologies

The application of nanomaterials in the development of LOC devices is important for

miniaturization, improving the sensor performance, enhancing electrical conductivity,

maintaining chemical stability, and offering biocompatibility. In LOC devices, nanoma­

terials based on metal, metal oxide, and carbon are applied for modification of sensor

platform to enhance the optical, electrochemical, and electrical performance. In the fol­

lowing section, the functions and capabilities of various types of nanomaterials for the

modification of sensor parts of the LOC devices are discussed.

5.3.1 Metal Nanomaterials

Metallic nanomaterials such as gold (Au), silver (Ag), platinum (Pt), and nickel (Ni) have

been used as a modifier of sensor platform in LOC devices owing to their advantages in

amplifying the signal of sensors. Among all types of metal nanomaterials, Au nanoma­

terials are the most commonly applied in various sensor applications. Au nanomaterials

are simple to make in a variety of sizes and shapes, easy to functionalize, compatible with

biomolecules, have great electrical conductivity, and excellent optical properties. Besides

that, Au nanomaterials are inert and stable against oxidation. The Au nanomaterials can

be synthesized via numerous physio-chemical and biological routes to vary the size,

shape, concentration, and surface chemistry [5]. The size and shape of Au nanomaterials

may greatly influence their optical properties.

The most common applications of Au nanomaterials are in labeling and colorimetric

assay in POC and LOC devices. Besides that, Au nanomaterials are commonly applied in

electrode modification for electrochemical sensors. Au nanomaterials have a large

surface-to-volume ratio that results in higher sensitivity and selectivity as well as en­

hancing the sensor response. The basic mechanism of Au nanomaterials in colorimetric

detection is based on the binding of target analyte with Au nanomaterials, which cause

aggregation. Generally, the Au nanomaterials are in red or pink color and change to

purple and blue when aggregated. The Au nanomaterials aggregation also is associated

with SPR peak shifts. This phenomenon occurs due to the enlargement of particle size of

Au nanomaterials, which alters the local electron confinement and causes the SPR peak

shifts [6]. Table 5.2 lists metal nanomaterials applied in LOC devices for various appli­

cations and detection techniques.

Zheng et al. [7] established a novel colorimetric biosensor for microfluidic LOC that

uses AuNPs as a labeling agent to detect different E. coli O157:H7 concentrations. Then,

the colorimetric biosensor is integrated with a smartphone imaging application (app) to

observe the AuNPs color changes. The colorimetric biosensor for microfluidic LOC has

been developed using 3D printing to fabricate the mold of the channel, silicone elastomer

kit to produce poly(dimethoxy)silane (PDMS) channel, and glass slide to bond with

PDMS channel. As shown in Figure 5.2a, the colorimetric biosensor for microfluidic

LOC consists of three components, the first component is the mixing channel for the

Nanomaterials and Lab-on-a-Chip Technologies

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