High-performance liquid chromatographic method for the simultaneous detection of the adulteration of cereal flours with melamine and related triazine by-products ammeline, ammelide, and cyanuric acid

Safeguarding Public Health: Advanced Detection of Food Adulteration Using Nanoparticle-Based Sensors

Food adulteration, whether intentional or accidental, poses a significant public health risk. Traditional detection methods often lack the precision required to detect subtle adulterants that can be harmful. Although chromatographic and spectrometric techniques are effective, their high cost and complexity have limited their widespread use. To explore and validate the application of nanoparticle-based sensors for enhancing the detection of food adulteration, focusing on their specificity, sensitivity, and practical utility in the development of resilient food safety systems. This study integrates forensic principles with advanced nanomaterials to create a robust detection framework. Techniques include the development of nanoparticle-based assays designed to improve the detection specificity and sensitivity. In addition, sensor-based technologies, including electronic noses and tongues, have been assessed for their capacity to mimic and enhance human sensory detection, offering objective and reliable results. The use of nanomaterials, including functionalized nanoparticles, has significantly improved the detection of trace amounts of adulterants. Nanoparticle-based sensors demonstrate superior performance in terms of speed, sensitivity, and selectivity compared with traditional methods. Moreover, the integration of these sensors into food safety protocols shows promise for real-time and onsite detection of adulteration. Nanoparticle-based sensors represent a cutting-edge approach for detecting food adulteration, and offer enhanced sensitivity, specificity, and scalability. By integrating forensic principles and nanotechnology, this framework advances the development of more resilient food-safety systems. Future research should focus on optimizing these technologies for widespread application and adapting them to address emerging adulteration threats.

How to Quantify the Adsorption of Cyanuric Acid on Activated Carbon Used from Swimming Pool Disinfection?

The physical and chemical characteristics of an adsorbent are key factors determining its efficiency in relation to a particular adsorbate molecule. The adsorption of cyanuric acid (cya) on activated carbon (AC) has not been extensively explored in terms of its basic phenomenon and specific surface interactions. Cya is an important molecule in the swimming pool industry, as it protects free chlorine from UV light degradation. A proper characterization of AC will be beneficial for swimming pool product suppliers to determine the criteria while purchasing it to remove excess cya accumulated in pools. A detailed investigation of the physicochemical properties of activated carbon was conducted to assess its potential to adsorb cya from water. The effect of the adsorption capacity under various pH conditions was studied and it was found that acidic pH favors the adsorption process. With the help of temperature-programmed desorption coupled with mass spectrometry (TPD-MS) and X-ray photoelectron spectroscopy (XPS), the surface chemistry was well analyzed for a proper understanding of the adsorbent-adsorbate interaction. While conventional pool test equipment gives inconsistent readings of the cya concentration, a UV-vis spectroscopy-based methodology has been developed to accurately measure traces of cya in water. This method can be helpful to validate the accuracy of pool-testers for research and development purposes. The batch adsorption experiments revealed that cya adsorption on activated carbon follows pseudo-second-order kinetics, which confirms that the adsorption mechanism is chemisorption, which in fact, depends highly on the surface chemistry of the AC and the reaction pH.

Elevated emissions of melamine and its derivatives in the indoor environments of typical e-waste recycling facilities and adjacent communities and implications for human exposure

Melamine and its derivatives are used as additives in flame retardants. Moreover, melamine-containing consumables such as laminates, adhesives, glues, and plastics are extensively used in electronic products. Nevertheless, there is no information concerning the identification of melamine and its derivatives during e-waste recycling. In the present study, the occurrence of melamine and three of its derivatives (cyanuric acid, ammelide, and ammeline) was identified for the first time in indoor dust from typical e-waste recycling areas and adjacent rural communities. Urban communities situated about 80 kilometers away were used as a control. The target analytes were detected in almost all the dust samples, which were dominated by melamine and cyanuric acid. The total concentrations of melamine and its derivatives varied among sampling locations in the following order: e-waste workshops (geometric mean: 15,018 ng/g) > urban houses (9060 ng/g) > local rural houses (6204 ng/g) > local streets (201 ng/g). This suggested that e-waste dismantling/recycling activities mainly contributed to the abundant emission of melamine and its derivatives in e-waste dust. Correlation analysis indicated that melamine and its derivatives were similarly applied in electronic products and e-waste recycling resulted in common emissions. The combined toxicity of melamine and its derivatives on human bladder cancer cells was observed. Importantly, Monte Carlo analysis was used to determine that the estimated daily intakes of these chemicals via dust ingestion for occupational e-waste recycling workers were 2.5-9 times higher than the estimated daily intakes for adult residents in both adjacent local communities and urban areas. These results are the first to demonstrate that e-waste dismantling workers are more vulnerable to the exposure risk posed by the presence of melamine and its derivatives in e-waste dust, which deserves more research attention.

Paper-based microfluidic devices for food adulterants: Cost-effective technological monitoring systems

Analytical sciences have witnessed emergent techniques for efficient clinical and industrial food adulterants detection. In this review, the contributions made by the paper-based devices are highlighted for efficient and rapid detection of food adulterants and additives, which is the need of the hour and how different categories of techniques have been developed in the past decade for upgrading the performance for point-of-care testing. A simple strategy with an arrangement for detecting specific adulterants followed by the addition of samples to obtain well-defined qualitative or quantitative signals for confirming the presence of target species. The paper-based microfluidics-based technology advances and prospects for food adulterant detection are discussed given the high-demand from the food sectors and serve as a valued technology for food researchers working in interdisciplinary technological frontiers.

"Aptamer-locker" DNA coupling with CRISPR/Cas12a-guided biosensing for high-efficiency melamine analysis

Herein, we report a method that combined "aptamer-locker" DNA with CRISPR/Cas12a-based biosensing for sensitive and rapid melamine analysis. Three strategies were harnessed for designing the DNA sensors that were well characterized by circular dichroism (CD) spectroscopy and isothermal titration calorimetry (ITC) in the absence and presence of melamine. The detection parameters were optimized to achieve good analytic performance. As a result, a limit of detection (LOD) as low as 38 nM was achieved, which is below the threshold (1.0 mg/kg) of allowable melamine in infant milk products. In addition, the sensors show high selectivity for melamine against other analogues such as cyanuric acid, ammeline and ammelide. Moreover, our method was effective for rapid melamine analysis in whole milk samples, with or without sample pretreatment, in less than 20 min. Adopting a commercially available portable fluorimeter, on-site analysis of melamine in milk was accomplished. The strategies demonstrated here can expand to detect other non-nucleic-acid targets by simply replacing the aptamers.

Simultaneous colorimetric and surface-enhanced Raman scattering detection of melamine from milk

We present a dual-mode readout sensing mechanism that can effectively distinguish true and false-positive signals of melamine in milk by combining colorimetric analysis and surface-enhanced Raman scattering (SERS) spectroscopy. The colorimetry analysis takes advantage of color change of plasmonic nanoparticles upon the presence of melamine. We discovered that Ag colloids with 20 nm diameter was suitable for both colorimetric and SERS methods. However, the colorimetric method may present false-positive signals with the presence of interfering compounds. SERS spectroscopy can overcome this limitation and directly obtain signature spectra from the same plasmonic NPs used for the colorimetric assay without any modification. Melamine/s-triazine can be reliably differentiated by probing the SERS spectra based on surface-selection rules. The limit of detection of sensing melamine from milk by this method could reached to 0.05 ppm. Therefore, the combination of colorimetric and SERS method not only allows for rapid preliminary screening of melamine by naked eyes, but also greatly reduces false-positive signals by surface selection rules in SERS.

New Ag-Doped COF Catalytic Amplification Aptamer Analytical Platform for Trace Small Molecules with the Resonance Rayleigh Scattering Technique

Covalent organic frameworks (COFs) and Ag-doped COFs (AgCOFs) are prepared by the polycondensation procedure and characterized by electron microscopy and molecular spectral techniques. Their catalysis of the Cu₂O particle reaction of glucose (GL)-Cu(II) was examined by resonance Rayleigh scattering (RRS), and AgCOFs were found to exhibit the strongest catalysis. The melamine (ML) aptamers (Apt_ML) can attach to the surface of AgCOF and inhibit its catalytic activity. When melamine (ML) is added to this reacting solution, Apt_ML-ML complexes are formed and the Apts are desorbed from the surface of AgCOF. As the concentration of ML increased, the catalytic activity of AgCOF increased and the RRS signal enhanced due to the increase in Cu₂O particles. When the ML concentration was in the range of 0.79-13.2 nmol/L, the RRS intensity increased linearly, with a detection limit of 0.72 nmol/L. When the Apts of urea and bisphenol A (BPA) were replaced by the Apt_ML, 66.7-1333 nmol/L urea and 0.33-2.7 nmol/L BPA, respectively, could also be determined, with detection limits of 30.4 nmol/L urea and 0.15 nmol/L BPA. Based on this, a new AgCOF amplification RRS method was established.

Rational design of MnO nanoparticles assemblies for sensitive magnetic relaxation detection of melamine

A versatile protocol has been developed for highly sensitive magnetic relaxation detection of the analyte based on the fabrication of MnO nanoparticles (NPs) assemblies. Based on the strategy that positively charged analyte could induce the assembly of negatively charged MnO NPs through electrostatic interaction, which will generate the change of magnetic relaxation rate of MnO NPs, we achieved highly sensitive and convenient detection of the analytes. By applying the detection of melamine as an example, we found that the detection limit can be as low as 0.733 ppb. Furthermore, this strategy has been applied for the initially detection of commercially available milk spiked with melamine as proof of its potential applicability of detection in complicated food samples.

Melamine Detection in Food matrices employing Chicken Antibody (IgY): A Comparison between Colorimetric and Chemiluminescent Methods

Background:

Melamine, contains 67% nitrogen by mass, and is adulterated in foods to uplift false protein. There is an urgent requirement to develop fast screening techniques for monitoring melamine in foods.

Objective:

To develop rapid, high throughput detection techniques for melamine in the food matrix.

Methods:

IgY antibodies were developed against melamine in the hen, isolated and used for detection of melamine. The detection by colorimetric and chemiluminescent methods was compared.

Results:

The detection range for melamine was 1 ng-25 µg by the colorimetric method and 10 fg/mL-25 ng/mL by the chemiluminescent method. There was a very low matrix effect, where the recovery was 86 to 106 % by colorimetric method and 71 to 98 % by the chemiluminescent method.

Conclusion:

Both colorimetric and chemiluminescent methods could be employed for the fast and consistent melamine detection in the food matrix.

Spatial and temporal trends of melamine and its derivatives in sediment from Lake Shihwa, South Korea

Occurrence, spatial distribution, and temporal trends of melamine and its derivatives (ammeline, ammelide, and cyanuric acid) were investigated in surface sediment and two sediment cores collected from Lake Shihwa, South Korea. ∑Melamine (sum of melamine and its three derivatives) was found in all surface sediment samples at concentrations that ranged from 16.6 to 4390 ng/g dry weight (dw), with an average value of 202 ng/g dw. ∑Melamine concentrations exhibited a clear spatial gradient, in decreasing order, as: creeks (mean: 577 ng/g dw) > inshore locations (41.9 ng/g dw) > offshore locations (24.3 ng/g dw). ∑Melamine concentrations were notably high in sediment collected near wastewater treatment plant (WWTP) outfalls. Melamine was the most prevalent compound in sediment collected from creeks (87%) and WWTP outfall locations (48%), whereas cyanuric acid was the dominant compound in sediment from inshore (51%) and offshore (63%) locations. The historical profiles of ∑Melamine in sediment cores corresponded with coastal development and environmental changes in this region. This is the first study to document the occurrence and temporal distribution of melamine in sediment cores, and this information is useful in understanding the fate of these relatively less-studied chemicals in the environment.

A nationwide survey of the occurrence of melamine and its derivatives in archived sewage sludge from the United States

Melamine-based resins are used extensively in laminates, plastics, coatings, glues, and dinnerware. Little is known, however, about the occurrence of melamine and its derivatives in the environment. In this study, a nationwide survey of melamine and its derivatives, namely ammeline, ammelide, and cyanuric acid, was conducted, using archived sewage sludge samples collected from 68 wastewater treatment plants in the United States (U.S.). The sum concentrations of four target compounds in sludge ranged from 34 to 1800 ng/g dry weight (dw), with a mean concentration of 240 ng/g dw; melamine (46%) and cyanuric acid (40%) collectively accounted for 86% of the total mass of analytes. No significant geographical variation in the concentrations of melamine and its derivatives in sewage sludge was found. The estimated emission of melamine and its derivatives via land-application of sludge was approximately 1600 kg/yr in the U.S. The hazard quotient values for melamine in sludge-amended soils ranged from 2.2 × 10^-5 to 4.4 × 10^-3, indicating that the current levels of melamine in sludge pose a minimal risk to the soil environment.

One-step wet-chemical synthesis of ternary ZnO/CuO/Co3O4 nanoparticles for sensitive and selective melamine sensor development

Using one-step wet-chemically synthesized ternary ZnO/CuO/Co₃O₄ nanoparticles (NPs) fabricated GCE sensor probe, a selective and sensitive melamine chemical sensor was developed by electrochemical approach, which exhibited the highest sensitivity, better repeatability, broad linear dynamic range, good linearity, fast response time, and lowest detection limit.

Simple and Label-Free Fluorescent Detection of Melamine Based on Melamine⁻Thymine Recognition

In the past few years, melamine has been illegally added into dairy products to increase the apparent crude protein levels. If humans or animals drink the milk adulteration of melamine, it can form insoluble melamine–cyanurate crystals in their kidneys which causes kidney damage or even death. In the present work, we constructed a simple and label-free fluorescent method for melamine detection based on melamine-thymine recognition. SYBR Green I was utilized as a reporter for this method as it did not require any modification or expensive equipment. In the absence of melamine, polythymine DNA was digested by Exo I, which caused a decrease in the fluorescence signal. In the presence of melamine, the polythymine DNA was able to fold into a double chain structure, however this was done with the help of T-melamine-T mismatches to prevent degradation. Then, the SYBR Green I combined with the double-stranded DNA to result in an intense fluorescence signal. The limit of detection in this method was 1.58 μM, which satisfied the FDA standards. This method also had a good linear relationship within the range of 10–200 μM. In addition, this new method has a good selectivity to distinguish melamine from the component of milk. As a result, we developed a simple and highly selectivity method for melamine detection.

Non-targeted NIR spectroscopy and SIMCA classification for commercial milk powder authentication: A study using eleven potential adulterants

A non-targeted detection method using near-infrared (NIR) spectroscopy combined with chemometric modeling was developed for the rapid screening of commercial milk powder (MP) products as authentic or potentially mixed with known and unknown adulterants. Two benchtop FT-NIR spectrometers and a handheld NIR device were evaluated for model development. The performance of SIMCA classification models was then validated using an independent test set of genuine MP samples and a set of gravimetrically prepared mixtures consisting of MPs spiked with each of eleven potential adulterants. Classification models yielded 100% sensitivities for the benchtop spectrometers. Better specificity, which was influenced by the nature of the adulterant, was obtained for the benchtop FT-NIR instruments than for the handheld NIR device, which suffered from lower spectral resolution and a narrower spectral range. FT-NIR spectroscopy and SIMCA classification models show promise for the rapid screening of commercial MPs for the detection of potential adulteration.

Triplex DNA formation-mediated strand displacement reaction for highly sensitive fluorescent detection of melamine

Since melamine is a strong hazard to human health, the development of new methods for highly sensitive detection of melamine is highly desirable. Herein, a novel fluorescent biosensing strategy was designed for sensitive and selective melamine assay based on the recognition ability of abasic (AP) site in triplex towards melamine and signal amplification by Mg²⁺-dependent DNAzyme. In this strategy, the melamine-induced formation of triplex DNA was employed to trigger the strand displacement reaction (SDR). The SDR process converted the specific target recognition into the release and activation of Mg²⁺-dependent DNAzyme, which could catalyze the cleavage of fluorophore/quencher labeled DNA substrate (FQ), resulting in a significantly increased fluorescent signal. Under the optimal conditions, the fluorescent signal has a linear relationship with the logarithm of the melamine concentration in a wide range of 0.005-50 μM. The detection limit was estimated to be 0.9 nM (0.1ppb), which is sufficiently sensitive for practical application. Furthermore, this strategy exhibits high selectivity against other potential interfering substances, and the practical application of this strategy for milk samples reveals that the proposed strategy works well for melamine assay in real samples. Therefore, this strategy presents a new method for the sensitive melamine assay and holds great promise for sensing applications in the environment and the food safety field.

A Surface Plasmon Resonance-Based Optical Fiber Probe Fabricated with Electropolymerized Molecular Imprinting Film for Melamine Detection

Molecularly imprinted polymer (MIP) films prepared by bulk polymerization suffer from numerous deficiencies, including poor mass transfer ability and difficulty in controlling reaction rate and film thickness, which usually result in poor repeatability. However, polymer film synthesized by electropolymerization methods benefit from high reproducibility, simplicity and rapidity of preparation. In the present study, an Au film served as the refractive index-sensitive metal film to couple with the light leaked out from optical fiber core and the electrode for electropolymerizing MIP film simultaneously. The manufactured probe exhibited satisfactory sensitivity and specificity. Furthermore, the surface morphology and functional groups of the synthesized MIP film were characterized by Atomic Force Microscopy (AFM) and Fourier transform infrared microspectroscopy (FTIR) for further insights into the adsorption and desorption processes. Given the low cost, label-free test, simple preparation process and fast response, this method has a potential application to monitor substances in complicated real samples for out-of-lab test in the future.

Nanopillar Filters for Surface-Enhanced Raman Spectroscopy

We present a simple, robust, and automated molecule extraction technique based on a centrifugal microfluidic platform. Fast and facile extraction of a food adulterant (melamine) from a complex sample medium (milk) on a SERS substrate is demonstrated. The unique characteristic of the detection method is the obtained "filter paper/chromatographic" effect which combines centrifugal force and wetting properties of the SERS substrate. The work addresses issues related to SERS-based detection of analytes in complex media, which is important for realizing next generation SERS platforms applicable for a broad variety of real-life applications.

Triplex DNA-based Bioanalytical Platform for Highly Sensitive Homogeneous Electrochemical Detection of Melamine

Melamine detection has attracted much attention since the discovery of the damage of melamine to human health. Herein, we have developed a sensitive homogeneous electroanalytical platform for melamine detection, which is relied on the formation of triplex molecular beacon integrated with exonuclease III (Exo III)-mediated signal amplification. The formation of triplex molecular beacon was triggered by the recognition and incorporation of melamine to the abasic (AP) site contained in the triplex stem. The stem of the triplex molecular beacon was designed to have a protruding double-strand DNA, which can be recognized and hydrolyzed by Exo III for releasing methylene blue (MB)-labeled mononucleotide. These released MB molecules exhibit high diffusivity toward indium tin oxide electrode with negative charge, thus producing a significantly increased electrochemical response. Taking advantages of the high binding affinity of the DNA triplex structure containing AP sites towards melamine and the unique features of Exo III, this sensing platform is capable for sensitive and selective melamine assay with a detection limit as low as 8.7 nM. Furthermore, this strategy shows good applicability for melamine assay in real samples. Therefore, this strategy broadens the application of triplex DNA and presents a new method for sensitive detection of melamine.

Interlaboratory validation of an LC-MS/MS method for the determination of melamine and cyanuric acid in animal feed

Melamine and cyanuric acid have been mixed illegally into food and feed to increase the nitrogen content, which results in deceptively high protein contents. As a consequence, a maximum level for melamine of 2.5 mg kg-1 feed was established by the European Union under Directive 2002/32/EC. The Technical Committee (TC) 327 of the European Committee for Standardisation (CEN) commissioned the standardisation of a method for the analysis of melamine and cyanuric acid in animal feed. One main task in the standardisation process is the performance of a full international collaborative trial, which is described in this paper. After performing a pre-trial study, in the main study eight different feed samples with different concentration levels of melamine and/or cyanuric acid were distributed as double-blind samples to 13 participants. The minimum criterion of eight laboratories submitting results per sample is fulfilled for melamine but only partly for cyanuric acid. The evaluation showed for both analytes a Horwitz ratio (HorRat) well below 2, and meets the requirements stated in the appropriate international protocols. The results demonstrated that the method seems to be suitable for the analysis of melamine and cyanuric acid in animal feed.

Controllable preparation of a hydrophilic/ion-exchange mixed-mode stationary phase by surface-initiated atom transfer radical polymerization using a mixture of two functional monomers

Mixed-mode chromatographic stationary phases require functionalization with at least two functional groups to yield multiple interactions with analytes. Departing from reported methods, a mixture of two different monomers, glycidyl methacrylate and 2-dimethylaminoethylmethacrylate, was grafted onto the surface of silica by a one-step surface-initiated atom transfer radical polymerization to prepare a novel hydrophilic interaction/anion-exchange mixed-mode chromatographic stationary phase. The grafted amounts of functional groups were controlled via varying the ratio of monomers in the polymerization system. The influences of water content, salt concentration and pH in the mobile phase were investigated to illustrate the mixed interaction between the stationary phase and analytes. The retention of various solutes on three columns, especially acidic and basic solutes, showed an obvious dependence on the ratio of the two monomers in the polymerization system. The results indicated that the strategy proposed in this work was beneficial to develop various types of mixed-mode chromatographic stationary phases with adjustable selectivity to meet the needs of complex samples. Finally, the column was successfully employed in the isolation of melamine in liquid milk.

Chemical and Biological Sensing Using Diatom Photonic Crystal Biosilica With In-Situ Growth Plasmonic Nanoparticles

In this paper, we described a new type of bioenabled nano-plasmonic sensors based on diatom photonic crystal biosilica with in-situ growth silver nanoparticles and demonstrated label-free chemical and biological sensing based on surface-enhanced Raman scattering (SERs) from complex samples. Diatoms are photosynthetic marine micro-organisms that create their own skeletal shells of hydrated amorphous silica, called frustules, which possess photonic crystal-like hierarchical micro- & nanoscale periodic pores. Our research shows that such hybrid plasmonic-biosilica nanostructures formed by cost-effective and eco-friendly bottom-up processes can achieve ultra-high limit of detection for medical applications, food sensing, water/air quality monitoring and geological/space research. The enhanced sensitivity comes from the optical coupling of the guided-mode resonance of the diatom frustules and the localized surface plasmons of the silver nanoparticles. Additionally, the nanoporous, ultra-hydrophilic diatom biosilica with large surface-to-volume ratio can concentrate more analyte molecules to the surface of the SERS substrates, which can help to detect biomolecules that cannot be easily adsorbed by metallic nanoparticles.

Colorimetric determination of melamine in milk using unmodified silver nanoparticles

Melamine is nitrogen rich chemical compound used as an adulterant in dairy products by unscrupulous people to increase the apparent protein content. This incident prompted the researchers to develop simple methods for easy detection of melamine in food samples. In the present paper, we report a simple and sensitive colorimetric method for detection of melamine in milk based on silver nanoparticles. This method relies upon the principle that melamine causes the aggregation of silver nanoparticles, resulting in abrupt color change from yellow to red under optimized conditions. The concentration of melamine in adulterated sample can be quantitated by monitoring the absorption spectra of silver nanoparticles using ultraviolet-visible (UV-Vis) spectrometer. The present colorimetric method which utilizes silver nanoparticles of 35 nm can reliably detect melamine down to a concentration of 0.04 mg l(-1).

Turn-on fluorescent detection of melamine based on Ag nanoclusters–Hg2+ system

The blue-emissive Ag nanoclusters could be quenched by Hg²⁺ and recovered by melamine.

Label-free fluorescence detection of melamine with a truncated aptamer

The 88 nt melamine aptamer Rd29C33 was truncated to a 34 nt Rd29C33-T7, which is suitable for the label-free detection of melamine.

Portable Detection of Melamine in Milk Using a Personal Glucose Meter Based on an in Vitro Selected Structure-Switching Aptamer

Melamine detection in milk and other foods has attracted much attention since the discovery that melamine-adulterated food causes severe kidney damage. Although many methods have been developed to detect melamine, few methods can provide quantitative results using an affordable and portable device that is suitable for home use or field application. To achieve this goal, we herein report the first in vitro selection of a melamine responsive aptamer using a structure-switching method. A personal glucose meter (PGM) based melamine sensor was designed and subsequently tested using the newly isolated aptamer. Conversion of melamine concentration to glucose amount was achieved by including an invertase-conjugated DNA that is complementary to part of the aptamer. Melamine binding triggers the release of the invertase-DNA conjugate, which hydrolyzes sucrose into glucose. The glucose produced is then measured directly using an off-the-shelf PGM. The described sensor shows high selectivity for melamine against several closely related melamine analogues, such as cyanuric acid, ammeline, and ammelide, and has low detection limits of 0.33 μM (or 41.1 ppb) in buffer and 0.53 μM (or 67.5 ppb) in 80% whole milk without any pretreatment. The detection limits meet the threshold of 2.5 ppm for non-infant-formula products and 1 ppm for melamine in infant milk products as defined by the U.S. Food and Drug Administration (FDA). In addition to the PGM sensor demonstrated here, the same aptamer can be converted into other types of sensors with different signal outputs, allowing portable detection of melamine under a variety of conditions.