contained a microchannel, reservoir, and inlet hole. The transparent glass slide was used

to attach the channel. The AgNPs could enhance the storage capacity, electrical con­

ductivity, and electrocatalytic properties, while chitosan may provide hydrophilicity and

functional group for hydrogen binding with amine and hydroxyl group. The AgNPs/

Chitosan/PGE electrode showed high storage capacity of 367.16 mF/cm² and a current

density of 1 mA/cm² with high cyclic stability of more than 1,500 charge-discharge cy­

cles. As for electrochemical sensors in H2O2 detection, the microfluidic AgNPs/Chitosan/

PGE had linear detection of 1-10M and LOD of 0.52M.

PtNPs have also been utilized for the development of LOC devices. The microfluidic

LOC for vitamin B detection was developed based on chemiluminescence (CL) of luminol

[16]. In their work, PtNPs acted as a catalyst to enhance the luminol CL signal caused by

the oxidation of AgNO3. With the presence of vitamin B, the CL of luminol signal in­

tensity increased. The microfluidic LOC was fabricated using soft lithography of the

PDMS with four sample inlets and one sample outlet. The microfluidic LOC for vitamin

B detection has the linear detection in the range of 1.0 × 10⁻⁷ to 4.0 × 10⁻⁵ mol/L and LOD

of 4.8 × 10⁻⁹ mol/L. In addition, an interesting LOC device which consists of two plat­

forms for pesticide atrazine (Atz) detection and degradation was developed by Sánchez

et al. [17]. The enzymatic activity of the boron-doped diamond (BDD) electrodes modified

with PtNPs and horseradish peroxidase (HRP) in Atz detection was evaluated using the

chronoamperometry technique. The PtNPs had improved the catalytic activity of the HRP

enzymatic reaction. The magnetic beads were integrated into the LOC device to pre-

concentrate and direct the sample into the microchannel. Meanwhile, the degradation of

the Atz pesticide was conducted using anodic electrochemical oxidation where the un­

modified BDD electrode acted as the anode, carbon electrode as the cathode, and Ag/

AgCl as the reference electrode. In the anodic electrochemical oxidation, the oxidation

of water produced hydroxyls radicals (HO·) on the BDD anode surface. The produced

HO· radicals subsequently reacted with the Atz pesticide and caused degradation.

The Atz LOC chip showed a linear response in the range of 0.9–4.5 nM and a very low

LOD of 3.5 pM.

5.3.2 Metal Oxide Nanomaterials in Lab on Chip

Metal oxide (MO) nanomaterials have been explored for modification of sensor platforms

in LOC devices. The MO nanomaterials exhibit high surface area, excellent electron-

transfer kinetics, inexpensive to produce, and have effective catalytic properties, making

them an excellent choice for signal enhancing in optical, electrochemical, and electrical-

based LOC devices. Metal oxides such as ZnO, CuO, Fe3O4, SnO2, MnO2, ZrO2, TiO2, and

MgO have been applied as sensor modifiers of the LOC devices for various applications.

Table 5.3 lists the metal oxide nanomaterials applied in LOC devices for various appli­

cations and detection techniques. Among all MO nanomaterials, ZnO nanomaterial is of

interest for a range of sensors such as gas, biological, and electrochemical sensors. ZnO

has excellent electrical, catalytic, and optical properties. ZnO is classified as a semi­

conductor in groups II–VI, which exhibits a direct bandgap ~3.37 eV. In principle, one-

dimensional (1-D) ZnO nanostructures (nanorods, nanowires, and nanotubes) are more

favorable because the structures may facilitate efficient carrier transport. This happens

because of 1-D ZnO nanomaterial has decreased grain boundaries, surface defects, dis­

orders, and discontinuous interface [19].

Most commonly, ZnO nanorods (ZnO NR) have been extensively studied for gas sensor

applications. The reason is that ZnO NR is an excellent chemiresistive material. The

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