nano-honeycomb SERS-based active chip for determining LCA from HCC patients. SERS-

active chips have a large surface area for AFP and AFP-L3 specific detection. The as-

fabricated chip accurately performs in the linear range of 0.003–3 ng/mL and has

potential in the clinical diagnosis of HCC [26].

8.6 Colorimetric Assay

The colorimetric assay detects biomarkers based on color. Substrates convert to colored

molecules via the interaction of the enzyme with antibodies. Enzyme brings specificity

while sensitivity is controlled by the signal amplification [27,28].

Dietary macronutrients are linked to health and their imbalance leads to diseases in­

cluding obesity, diabetes, cardiovascular disease, metabolic disease, and cancer. Volatile

compounds released from the human body provide information on metabolic processes.

Volatile biomarkers are correlated to dietary macronutrients intake. Volatile biomarkers

are selectively and sensitively identified through the calorimetric assay of biofluids.

Calorimetric assays/sensors are low cost and detect the color change after the chemical

reaction of the analyte with the sensing molecule. This assay is capable of multiplexed

analysis with qualitative and semi-quantitative detection. In a study, a transdermal volatile

biomarker detection system was built for the calorimetric sensing of dietary macronutrients

explained in Figure 8.3. The study finds that the transdermal acetone levels increase after

the usage of keto-acids while levels decrease after the carb-rich-diet intake. The calorimetric

sensor exhibits a linear range from 0 to 40 ppm. The as-fabricated calorimetric sensor can

be used in laboratories and hospital settings for nutrient-related disease monitoring and

disease management [29].

8.7 Electrochemical Assay

The electrochemical assay is based on the electrode potential, interfacial capacitance, im­

pedance, and oxidation-reduction current. Electrochemical assays have fast response, low

cost, high sensitivity, selectivity, accuracy, and reliable properties for the detection and

quantification of biomarkers [30]. Micro-RNAs (miRNA) are the endogenous non-coding

short RNAs and regulate gene expression. miRNA in cancer cells act as diagnostic

FIGURE 8.3

Calorimetric detection of macronutrients by the use of a transdermal volatile biomarker detection system.

Adapted with permission [ 29], Copyright (2022), Elsevier.

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