Graphene Oxide Xanthine Biosensor for Meat Spoilage - University of Florida, 2014

Vanegas, D. C., Gomes, C., & McLamore, E. S. (2014). Xanthine oxidase biosensor for monitoring meat spoilage. *SPIE Proceedings*. https://doi.org/10.1117/12.2050489

SPIE Proceedings · 2014

University of Florida researchers used ACS Material graphene oxide in a Pt/Ir xanthine oxidase biosensor that detects meat spoilage with a 150 nM detection limit.

About this research

Researchers at the University of Florida, working with collaborators at Texas A&M University and Universidad del Valle, developed an electrochemical xanthine oxidase biosensor for real-time monitoring of meat spoilage using graphene oxide supplied by ACS Material as a core component of a nanomaterial 'sandwich' on a platinum-iridium electrode. The completed biosensor detected xanthine with a sensitivity of 2.14 ± 1.48 µA/mM, a response time of 5.2 ± 1.5 seconds, a lower detection limit of 150 ± 39 nM, and retained at least 88% of its activity after seven days of continuous use. The work was published in SPIE Proceedings Vol. 9107 in 2014.

Meat spoilage is driven by bacterial degradation of ATP into inosine, hypoxanthine, and finally xanthine. The ratio of these breakdown products to total ATP-related compounds defines the K-value, the standard freshness index used in the meat industry. Conventional K-value assays rely on chromatographic analysis that is slow, expensive, and unsuited to point-of-use screening in slaughterhouses, distribution centers, or retail. A rapid, low-cost electrochemical biosensor that selectively measures hypoxanthine and xanthine would let food processors and inspectors flag contaminated product before it reaches consumers. Beyond food safety, the same sandwich-electrode architecture is broadly applicable to oxidase-based biosensing for clinical diagnostics, water quality monitoring, and bioprocess control, where rapid measurement of metabolites tied to hydrogen peroxide generation is required.

The ACS Material graphene oxide was used as the matrix for the central transduction layer. The team prepared a CeO/rGO suspension by mixing cerium oxide nanoparticle dispersion, the ACS Material GO, and L-ascorbic acid in a 1 mL : 2 mg : 8 mg ratio, ultrasonicating for 30 minutes so that ascorbic acid reduced the GO to reduced graphene oxide (rGO) in situ around the nanoceria. A 2 µL aliquot of this suspension was spin-coated at 2600 rpm for 7 minutes onto a Pt/Ir working electrode (1.6 mm tip diameter) that had already been decorated with amorphous platinum nanoclusters by sonoelectrodeposition at 10 V in 1.44% chloroplatinic acid. A second layer of platinum black was then sonoelectrodeposited on top of the CeO/rGO film, completing the nPt–rGO/CeO–nPt sandwich. Xanthine oxidase was finally encapsulated in laponite hydrogel and silica sol-gel and drop-cast onto the nanomaterial stack. In this architecture, the ACS Material-derived rGO provides the conductive scaffold that bridges nPt junctions and supports the catalytic nanoceria.

Cyclic voltammetry in 4 mM Fe(CN)6/1 M KNO3 confirmed reversible redox behavior on the modified electrode. Using the Randles-Sevcik equation, the electroactive surface area of the nanomaterial-modified probe was calculated as 0.062 ± 0.008 cm², about a 226% increase over the bare Pt/Ir tip. SEM images (FEI XL-40 FEG-SEM) showed that the nPt/rGO/CeO stack created a rough, high-area topography with strong contact between the electrode and the electrolyte. DC potential amperometry at +500 mV vs. Ag/AgCl produced clear, stepwise current increases with each xanthine injection, giving a linear calibration curve with sensitivity of 2.14 ± 1.48 µA/mM and a 5.2 ± 1.5 s response time. The detection limit of 150 ± 39 nM is well below the xanthine concentrations associated with early-stage spoilage. Continuous use for seven days showed that the sensor retained 88% of its initial sensitivity, indicating that the laponite/sol-gel matrix effectively stabilized the xanthine oxidase. Selectivity testing against urea, glucose, and ascorbic acid showed that only ascorbic acid produced significant interference; the authors note that a Nafion ion-exchange overlayer is the standard remedy.

The results point toward a practical handheld K-value meter for the meat supply chain. Sub-micromolar detection, fast response, and week-long operational stability are the three attributes that matter most for in-line spoilage screening, and this device delivers on all three. Beyond meat freshness, the same 

nanoceria/rGO/Pt black sandwich is a generic transducer platform for any oxidase enzyme that generates H2O2, opening applications in glucose monitoring, lactate sensing for sports physiology, neurotransmitter detection, and on-chip bioreactor monitoring. The authors highlight Nafion integration to suppress ascorbic acid interference as the natural next step, along with miniaturization toward disposable single-use probes.

For researchers building oxidase-based electrochemical biosensors, this study illustrates how a commercial graphene oxide starting material can be converted on-electrode into a functional rGO conductive layer, removing the need for in-house GO synthesis. Graphene oxide is available from ACS Material in several formats — single-layer powders, dispersions, and high-density grades — suitable for similar nanocomposite electrode work in food safety, biomedical, and environmental sensing applications.

How ACS Material products were used

• Graphene Oxide (GO) (Graphene Series)  — “Graphene oxide (GO) was obtained from ACS Material (Medford, MA)”

Product Performance in this Study

Graphene oxide from ACS Material was reduced in situ with ascorbic acid and combined with nanoceria and platinum black to form the conductive nanomaterial 'sandwich' on the Pt/Ir electrode tip. The composite increased the electroactive surface area by ~226% over a bare electrode, enabling fast amperometric transduction with a 150 nM detection limit for xanthine.

Related product categories

• Graphene Series

Frequently asked questions

How is graphene oxide used in a xanthine oxidase biosensor for meat spoilage?

Graphene oxide is mixed with cerium oxide nanoparticles and ascorbic acid, then ultrasonicated so the ascorbic acid reduces the GO to rGO in situ around the nanoceria. The suspension is spin-coated onto a Pt/Ir electrode already coated with platinum black, then a second platinum black layer is added, forming a conductive sandwich. Xanthine oxidase encapsulated in laponite hydrogel sits on top for biorecognition of hypoxanthine and xanthine.

What detection limit can a graphene oxide xanthine biosensor achieve for meat freshness monitoring?

The biosensor described in this study reached a lower detection limit of 150 ± 39 nM xanthine with a sensitivity of 2.14 ± 1.48 µA/mM and a response time of 5.2 ± 1.5 seconds. It retained at least 88% of its initial activity after seven days of continuous use, which is well within the range needed to flag early-stage bacterial spoilage of meat samples in food-safety screening applications.

Why combine reduced graphene oxide with nanoceria and platinum black on a biosensor electrode?

The three materials play complementary roles. Platinum black nanoclusters create catalytic junctions and high surface roughness. Reduced graphene oxide bridges those junctions and provides a continuous conductive scaffold. Nanoceria boosts catalysis of hydrogen peroxide and superoxide, the reactive oxygen byproducts of oxidase enzymes. Together they raised the electroactive surface area by about 226% over a bare Pt electrode and enabled fast, low-noise amperometric detection.