Table 3.

Detection methods for improved sensing capabilities in food samples

Detection type	Type of LOC	Unique characteristics	Food sample	Conditions	Conclusions	References
Electrochemical detection	Impedance LOC	The cell membrane of the sample prevents the electric field lines from penetrating the cell. When a signal frequency is applied, the total impedance decreases due to short-circuiting. The properties of the sample can then be evaluated	Cow milk	Amplitude: 100 mV Frequency range: 100 Hz–1 MHz	Analysis of impedance and conventional measurements indicate that the former can be used to sense the presence of soap adulteration of 0.9% toxicity in milk	Brazey et al. (2018), Das et al. (2018)
	Carbon nanotube LOC	Such LOCs can be used to minimize the contact surface between microfluidic device channels giving higher precision during fluid control. The unique characteristic of this type of LOC is its electronic properties, higher sensitivities, and lower voltages	Vegetable extracts	Solution concentration: 4.75 × 10–5 mol/L Current: 4 A pH: 5	Composite carbon paste (60:40 w/w) and paraffin binder gave the best results. The device proved effective in detecting pesticides, vitamins, and pro-vitamins thus showing high activity and catalytic properties	Oliveira et al. (2013), Ghasemi et al. (2017)
Optical detection	Lateral flow assay (or dipstick assay)	Simplest form of sensing technology. First applied during pregnancy tests. The user either applies the drop of sample onto the strip or dips the strip into the liquid sample. This causes a reaction between the strip and sample showing color changes, or line	Corn	Dissolving solution: tris-HCl (10 mL) pH: 8.5 Concentration of corn sample: 3,10, 30 ng/mL	Improvement in the recovery of mycotoxins in corn samples from 96.4 to 104.67%	Zhang et al. (2018)
			Drinking water	Pesticide samples were diluted with 1 mg/mL acetonitrile, 5 mM phosphate buffer. pH: 7 Storage temperature: 4ºC	Lateral flow sensors showed the rate of inhibition reaction. Rate was determined by sensor output system. The calibration curve obtained for chlorpyrifos was 2–45 µg/L and for carbaryl, 0.24–2 µg/L. Reproducibility obtained was 4.2–5%. No specific sample preparation was required	Fernández-Ramos et al. (2020)
	ELISA LOC	Generally performed on a microplate. The target solution continuously flows into the microchannel. This continuous flow makes the rinsing very effective and detects pathogens	Potato and corn chips	Amount of sample taken: 1 g Incubation temperature and time: 50 °C for 60 min	Analytical recovery for detection of acrylamide in potato and corn chips: 91.8% to 96%. Limit of detection: 5 ng/mL. High specificity with the technique having the potential for quick, simple, and reliable screening analysis	Franek et al. (2014)
			Gluten-free pieces of bread, sandwich spreads, and fried foods	Sample size: 0.25 g to 1 g	An evaluation of gluten cross-contact was done. 93.6% of results showed no significant cross contacts	Parsons et al. (2020)
	Surface plasmon resonance LOC	Unique technology involving no labeling step with multiple rinsing as compared to lateral flow assay and ELISA. Surface plasmon resonance uses the total internal reflection principle causing variation in the refractive index of metal and liquid. The sample detection is done using concepts of polarization and oscillations	Milk	Limit of detection: 0.164 µg/mL	Antibody capturing using the sensor. This method proved better as compared to the ELISA-based technique for food allergen risk management in food manufacturing	Ashley et al. (2018)
			Peanut	Limit of detection: 5.54 ng/mL	Polyclonal antibodies enhanced the sensitivities using surface plasmon resonance and proved as a better method of detection as compared to ELISA	Wu et al. (2016), Zhou et al. (2019)
PCR detection	Stationary chamber PCR	The technology uses heat transfer principles. The sample is heated at different temperatures to achieve thermocycling. The volume taken is the least (in microliters) thus yielding a faster heat transfer. Generally used for detecting pathogens or adulterants in foods	Meat mixtures	Initial activation: 95 °C for 5 min Denaturation: 95 °C for 15 s Annealing: 60 °C at 15 s Extension: 72 °C for 10 s	Pork DNA detection in binary meat mixtures was conducted using conventional and real-time PCR. Real-time PCR detected pork DNA at 0.0001 ng/µL or less. Detection limits of pork DNA in meat mixtures were 0.22, 0.047, 0.048, 0.015 ng/µL	Al-Kahtani et al. (2017)
			Cashew	Limit of detection: 10 ppm Initial boiling: 121 °C for 15 min and 135 °C for 30 min	Real-time PCR detection proved better as compared to ELISA. Boiling did not affect cashew detectability	Sanchiz et al. (2018)
	Isothermal PCR LOCs	The principle of isothermal PCR is based on the amplification of a target sample under a specific temperature. The technique is fast, ultrasensitive, and takes place within a single step. Monitoring is then generally done using a fluorescent reader. Much easier to fabricate and operate as compared to real-time PCR	Salmonella in Chicken	Sample usage: 1 mL Time: 5 h Temperature for enrichment: 42 °C	Isothermal PCR required less expertise, was economical and reliable. It proved a rapid testing tool for interpretation. Detection time was obtained in less than 8 h including enrichment and DNA extraction steps	Tsen et al. (2013), Kumar (2021)
Colorimetric detection	Tree-shaped self-calibrating device	Widely applied for the analysis of proteins, chemicals, and metals. This tree-shaped device integrates self-calibration on the test strip due to which effects of environmental conditions can be minimized	Proteins	Bovine serum assay usage: 0–5 mg/mL	The device showed its potential to be coupled with digital transmission of images for remote sensing systems in food control and environmental analysis	Wang et al. (2010)
Chemiluminescence	Lab-on-paper device	Type of detection requiring less instrumentation and providing high sensitivity. Paper was chosen as a fabricating material considering cost efficiency for sample analysis	Cabbage leaves and tomato skin	Skins and leaves were washed using 20 mL distilled water for 40 s and then filtered before adding into analytical devices	Limit of detection of dichlorvos in the vegetables 0.8 ng/mL Sensitivity determination of dichlorvos in vegetables ranged between 3 ng/mL and 1 µg/mL making the technology a promising approach for environmental monitoring and food analysis	Liu et al. (2015), Al Mughairy and Al-Lawati (2020)

LOC: Lab-on-a-chip

ELISA: Enzyme-linked immunosorbent assay

PCR: Polymerase chain reaction

DNA: Deoxyribonucleic acid