Quantifying Copper Nanoparticles on Plant Leaves using Single-Particle ICP-MS

Importance of the Topic

Nanoparticle-based agrochemicals offer enhanced efficacy and reduced chemical use, but their environmental fate and residual presence on edible crops require reliable quantitative analysis. Quantifying copper nanoparticles on plant surfaces is essential for evaluating food safety, regulatory compliance, and understanding plant–nanoparticle interactions.

Objectives and Study Overview

This study employs single-particle ICP-MS to (1) detect and size copper oxide nanoparticles (nano-CuO) on leafy vegetables, and (2) quantify their removal by rinsing. Edible leaves (lettuce, collard green, kale) were exposed to standardized nano-CuO suspensions, rinsed, and the collected rinse waters analyzed in triplicate.

Methodology and Instrumentation

Sample Preparation:

• Leaf segments washed, exposed to 1 mg/L nano-CuO (20–100 nm) in 10 drops per sample.
• After 2 h drying, leaves rinsed three times with 10 mL deionized water; rinse solutions collected separately.
• Control samples prepared identically without nano-CuO.

Standards and Calibration:

• Uncoated nano-CuO standard (20–100 nm), hydrodynamic diameter 280 nm.
• Gold nanoparticles (60 nm) for nebulization efficiency determination.
• Copper ionic standard (1 µg/L) for element response factor.

Instrumentation:

• Agilent 7900 ICP-MS in single-particle mode with glass concentric nebulizer, quartz spray chamber, quartz torch.
• Fast Time-Resolved Analysis at 100 µs dwell time.
• Method Wizard via MassHunter software for automated parameter setup and data processing.

Main Results and Discussion

Control Analysis revealed background Cu-containing nanoparticles (20–50 nm) at low levels (30–90 ng/L).
Exposed samples exhibited first-rinse nano-CuO concentrations of 500–750 µg/L (collard green highest).
Particle size distributions showed median diameters of 30–35 nm in initial rinses; subsequent rinses yielded larger median sizes, indicating preferential removal of smaller particles.
Leaf surface characteristics influenced retention: rough, hydrophobic kale leaves retained more nanoparticles than smoother, hydrophilic lettuce leaves.
Residual nanoparticle levels after washing remained well below the EPA drinking water limit (1.3 mg/L).

Benefits and Practical Applications

spICP-MS offers simultaneous quantification of nanoparticle number concentration, size distribution, and dissolved ion concentration in a rapid, minimally prepared analysis. This approach supports:

• Evaluation of nanopesticide adhesion and wash-off efficiency.
• Monitoring of nanoparticle residues in agricultural produce.
• Assessment of environmental release and runoff in agronomic studies.

Future Trends and Opportunities

Integration of spICP-MS with complementary imaging (electron microscopy) and separation techniques could provide deeper insights into nanoparticle localization. Development of standardized protocols for diverse agrochemical nanomaterials and in situ monitoring of nanoparticle uptake in plant tissues will advance regulatory frameworks and sustainable nanotechnology applications.

Conclusion

Single-particle ICP-MS using the Agilent 7900 provides a robust, high-throughput method to quantify copper-based nanoparticles on plant leaves. The study demonstrates effective nanoparticle removal by washing and highlights the impact of leaf morphology on nanoparticle retention. These findings inform safer nanomaterial design and regulatory assessment in agriculture.

References

1. Montano MD, Olesik JW, Barber AG, Challis K, Ranville JF, 'Single particle ICP-MS: advances toward routine analysis of nanomaterials', Anal Bioanal Chem, 2016, 408, 5053–5074.
2. Sun X, Tabakman SM, Won-Seok S, Zhang K, Zhang G, Sherlock S, Bai L, Dai H, 'Separation of Nanoparticles in a Density Gradient: FeCo@C and Gold Nanocrystals', Angew Chem, 2009, 48, 939–942.
3. Trumbo P, Yates AA, Schlicker S, Poos M, 'Dietary reference intakes: vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc', J Am Diet Assoc, 2001, 101(3):294–301.
4. EFSA Panel on Dietetic Products, Nutrition and Allergies, 'Scientific Opinion on Dietary Reference Values for copper', EFSA J, 2015, 13(10):4253.
5. World Health Organization, 'Guidelines for drinking-water quality', 4th edition, 2011.
6. US EPA, 'National Primary Drinking Water Regulations (NPDWR)', accessed May 2018.
7. Adeleye AS, Conway JR, Perez T, Rutten P, Keller AA, 'Influence of extracellular polymeric substances on the long-term fate, dissolution, and speciation of copper-based nanoparticles', Environ Sci Technol, 2014, 48, 12561–12568.
8. Pace H, Rogers NJ, Jarolimek C, Coleman VA, Higgins CP, Ranville JF, 'Determining Transport Efficiency for the Purpose of Counting and Sizing Nanoparticles via Single Particle Inductively Coupled Plasma Mass Spectrometry', Anal Chem, 2011, 83, 9361–9369.