permits strong optical coupling in every direction of the incident light, thus enhancing the

sensitivity of AuNPs in SPR. The AuNPs integrated sensor chip for the detection of

Aflatoxin B1 (AFB1) detection using SPR equipment has been developed by Bhardwaj

et al. [9]. The AuNPs acted as SPR signal amplifiers and provided a larger area for im­

mobilization of anti-AFB1 antibodies. The Au chips were integrated with AuNPs con­

jugated with anti-AFB1 antibodies (AuNPs- anti-AFB1 Ab) as the target and analyzed

using the flow cell of the SPR-2 system. The AuNPs/anti-AFB1 antibodies/Au sensor

chips response linearly for AFB1 detection from 0.01 to 50 nM, and LOD of 0.003 nM.

Colorimetric and SPR sensor detection are also employed in heavy metal detection. The

portable heavy metal detection has been developed using AuNPs-based colorimetric

technique integrated into the LOC device for Pb(II) and Al(III) ions detection [10]. The

mechanism of detection is based on an aggregation of AuNPs caused by the chemically

functionalized AuNPs coordinate with metal ions, resulting in shifting of the AuNPs SPR

absorbance. The LOC device was developed by integrating the custom-made PDMS and

glass microwell plate for sample analysis with a hand-held colorimetric reader for

quantifying the absorbance shifting of the AuNPs solutions after reaction with heavy

metal ions. The hand-held colorimetric reader is made of a narrow-band light-emitting

diode (LED), photodiodes, printed circuit board, and microcontroller. The micro­

controller functions as a LED controller, measuring the voltage output of the photodiode

and transmitting measurement data to a computer. The developed portable LOC device

can detect the Pb(II) and Al(III) with LOD of 30 ppb and 89 ppb, respectively.

The LOC of ITO electrode modified with electrodeposited AuNPs as the modified WE,

Ag/AgCl as the RE, and ITO as the CE has been developed for online Hg(II) detection using

electrochemical technique [11]. The ITO electrode was patterned with a three-electrode

electrochemical system attached with a low volume cell. The AuNP/ITO on a chip was

developed by the sandwich method linked to automatic sample injection systems, po­

tentiostat, computer, and container for sample waste. The benefits of the AuNP/ITO on-

chip for heavy metal detection are the small size and portability of the device for on-site

measurement, one-step procedure due to automatic sample input using flow cell, and ac­

curacy of measurement due to undiluted sample. The AuNP/ITO on-chip showed good

electrochemical Hg(II) detection with a linearity of 0.63–80 ppb and LOD of 0.11 ppb.

Another metal nanomaterial that is widely applied in LOC devices is AgNPs. AgNPs

have excellent optical, electrical, and biological properties to improve the sensor per­

formance of the LOC device. AgNPs exhibits enhanced color visualization and high

sensitivity, especially in optical sensor applications. However, AgNPs require stabiliza­

tion or functionalization to provide colloidal stability, prevent aggregation and oxidation.

Commonly, AgNPs are functionalized with polymeric molecules such as polyvinyl

alcohol (PVA), polyethylene glycol (PEG), and polyvinylpyrrolidone (PVP) or surfactants

such as citrate and cetyltrimethylammonium bromide (CTAB). A microfluidic LOC de­

vice for protein biomarker thrombin detection was developed by Zhao et al. [13]. The

AgNPs-aptasensor was used as the labeling agent for specifically detecting the thrombin

protein on a glass/PDMS microfluidic LOC. The AgNPs calorimetric color changes were

quantified based on color shade grading or converted into grayscale value using a flatbed

scanner. The AgNPs yellow color faded as the concentration of thrombin decreased. This

happened because of the low AgNPs-aptamer complex present. The developed calori­

metric LOC was able to detect the thrombin protein with LOD of 20 pM.

Salve et al. [14] reported on 3D microfluidic LOC for the supercapacitor and electro­

chemical sensor for H2O2 detection. A pencil graphite electrode (PGE) has been used as

the electrode and was modified with AgNPs and chitosan. The microfluidic device

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