# A Review of Milk Frauds and Adulterations from a Technological Perspective
## 3 Results and Discussion
### Methods for Detecting Adulterants in Milk
#### 3.2.3. Instrumental Methods (Quantitative)
Another study to identify melamine is based on a portable surface plasmon resonance (SPR) biosensor, which is a non-invasive, label-free sensor that uses polarized electromagnetic waves to investigate real-time interactions between an analyte in solution and immobilized biomolecular recognition elements. The three types of immunoassay used in the study, namely the direct test, displacement test, and competitive test, demonstrated great selectivity for the chemical compound. The competitive test, which was completed in 15 min and had a detection limit of 0.02 g/mL, was the most efficient [59]. [PERSON] et al. created an aptamer-based biosensor for detecting melamine in raw milk. The procedure involved microarray-based screening and chemiluminescence detection to optimize the screened biosensor. At 2 mM melamine, the biosensor demonstrated considerably increased signal intensity [60]. [PERSON] et al. made possible the simple and rapid detection of melamine in milk by using a reusable fading-wave fiber optic biosensor. The complete test process, including regeneration, has thus been shown to take less than 15 min. Because of the surface chemistry of the melamine-bovine serum albumin conjugates on the probe surface, not only are immobilized melamine activities towards the antibody maintained, but non-specific adsorption is reduced by immersing the fiber surface in bovine serum albumin. In this study, cross-reactivity against organic molecules structurally related to melamine was low [61]. Several studies have been published on the detection of urea as an adulterant in milk utilizing biosensors. [PERSON] et al. have created a promising technique for determining melamine and urea in cow's milk samples. It was represented by an acetylcholinesterase collagenase cyclic voltammetric biosensor based on a Pt electrode modified with zinc oxide nanospheres. To examine the electrochemical changes on the biosensor electrode, cyclic voltammetry was used. The biosensor was subjected to testing with urea and melamine at levels ranging from 1 to 20 nM and was able to identify the adulterants down to 3 and 1 pM, respectively. The bioelectrode demonstrated 100% permeability to the binary combination of melamine and urea, which improved selectivity [55]. Entrapping the urease enzyme in a polymer matrix of poly (carbamoylsulphonate) (PCS) and polyethyleneimine (PEI) resulted in the development of a potentiometric biosensor for the detection of urea. The stand-alone urea biosensor device detects urea in milk samples using a screen-printed Ag/AgCl reference electrode. This biosensor was thus built to respond quickly and consistently to changes in test urea concentrations. Was utilized as well on unprocessed milk samples, with a limit of detection of 2.5 \(\times\) 10\({}^{-5}\) M/L [62]. [PERSON] et al. developed an Android-integrated biosensor system to identify fraudulently added urea in milk, improve health and consumer comprehension, and facilitate communication between the food testing laboratories and concerned authorities. As a result, data from a flow injection urea biosensor served as a point of contact for the analyst, the customer, and the appropriate higher authorities. Initially, adulterated milk samples were evaluated using the biosensor, and the results were saved on a computer. Once the data had been evaluated, it was transmitted to the analyst's Android phone in graphic form, with the response signal flow visible in real time. This tool can be successfully used in milk collection centers, individually by the consumer, or by authorities for data collection and long-term milk quality monitoring [63]. The use of a simple portable optical screening sensor provides a semi-quantitative method for detecting urea in milk. This sensor is made of air-stabilized lipid layers with urease inserted within them. Without this enzyme, lipid films became fluorescent when exposed to a UV lamp. A small amount of aqueous urea solution activated the fluorescence.