easily move to form the surface plasmon resonance (SPR) that is useful in providing sen­

sitive detection for optical sensors [6].

Metal oxide nanoparticles such as zinc oxide (ZnO), iron oxide (Fe3O4), manganese

oxide (MnO2), copper oxide (CuO), cerium oxide (CeO2), and titanium oxide (TiO2) are

applied as the signal enhancement for electrochemical sensors, biosensors, and electrical

devices. Metal oxide nanomaterials have excellent chemical, electrical, and physical

properties. The carbon-based nanomaterials, especially carbon nanotubes (CNT) and

graphene nanomaterials, show excellent properties in improving the sensing capability in

LOC devices owing to their changeable optical properties and bandgap energy, excellent

conductivity for electron transfer, and the novel structure. In this chapter, the authors aim

to provide an overview of the LOC design, detection techniques, and the role of nano­

materials in LOC devices applications. Additionally, the fabrication strategies, properties,

and sensing applications of nanomaterials in LOC technologies are discussed based on

excellent published works in recent research and future trends.

5.2 Lab-on-a-Chip Detection Technique

The transducers of the LOC devices can be classified into optical, electrochemical, and

electrical types. In optical-based LOC devices, the optical changes caused by the inter­

action of sample analyte with recognition element are analyzed in the form of color,

absorption, transmission, or emission of light. Commonly, the optical LOC devices are

categorized based on optical detection techniques such as calorimetry, surface plasmon

resonance (SPR), fluorescence, and chemiluminescence (CL). The optical detection in LOC

devices offers advantages of low LOD, suitable for various types of analytes, non-

destructive and rapid detection techniques. However, optical detection LOC devices

suffer limitations in the form of bulky and expensive optical equipment and interference

from the surrounding condition. The working principle of various transducers types,

detection techniques, and types of nanomaterials applied are summarized in Table 5.1.

As for the electrochemical-based LOC devices, the changes in the electrochemical re­

sponse caused by the interaction of sample analyte with recognition element are measured

in the form of amperometric (current), voltammetric (current), and impedance (impedi­

metric). In an electrochemical LOC device, the device is commonly fabricated with the

integration of a three-electrode system consisting of a working electrode (WE) as the sen­

sing platform, reference electrode (RE) acts as a reference in measuring the WE potential,

counter electrode (CE) to complete the current circuit, and a potentiostat to control the

potential difference between WE and RE. The function of nanomaterials in this type of

measurement is not limited to analyte labeling but also acts as a catalyst for the chemical

reaction. The advantages of electrochemical LOC devices are high sensitivity, low LOD,

high specificity, and low power requirement, which are suitable for miniaturization of the

LOC devices. However, the limitations of electrochemical LOC devices are the requirement

of redox elements to enhance the signal and interference from the surrounding condition.

In field-effect transistor (FET)–based LOC devices, the changes in conductance caused

by the interaction between analyte and recognition element are measured. The FET de­

tection technique is commonly composed of a semiconducting channel as the sensor

platform that connects the source and the drain electrodes. Any reaction that occurs on

the channel surface causes changes in the electric field that control the potential of a gate

Nanomaterials and Lab-on-a-Chip Technologies

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