Gelatin-based microdroplet calibration approach for the analysis of gold nanoparticles and essential elements in plant tissues by Laser Ablation-Single Particle Inductively Coupled Plasma-Time of Flight Mass Spectrometry

LA-spICP-ToFMS approach enables simultaneous AuNPs and elemental mapping in plant tissues with 100% transport efficiency.

Abstract Text:

The increasing global production and application of nanomaterials for industrial, agronomic, and biomedical purposes has led to the widespread release of nanoparticles (NPs) into the environment, raising concerns about their bioavailability, mobility, and potential risks to ecosystems and food safety. Among them, metallic NPs such as gold (AuNPs) can be taken up by plants, undergo biotransformation, and accumulate in edible tissues. Analytical approaches are required to assess their accumulation and spatial distribution in planta. Although single particle Inductively Coupled Plasma-Mass Spectrometry (spICP-MS) allows for the assessment of NPs biotransformation, it often requires enzymatic digestion procedures, which compromise the spatial distribution of individual particles and may even affect their integrity. In contrast, Laser Ablation-single particle Inductively Coupled Plasma-Time of Flight Mass Spectrometry (LA-spICP-ToFMS) is a cutting-edge technique that enables simultaneous mapping of NPs and dissolved elements in biomaterials based on direct solid sampling, while preserving their spatial distribution. In this work, a gelatin-based microdroplet calibration approach was developed for quantitative mapping of AuNPs and essential elements in plant tissues using LA-spICP-ToFMS. Gelatin-based microdroplets (0.015-0.100 mg) were manually deposited onto microscope slides and ablated using an Iridia laser system equipped with a low-dispersion tube-type cell and high-efficiency aerosol transport. Standards were spiked with 30, 50, and 100 nm AuNPs (8 × 10⁴ particles mg^-1) and 1 µg g^-1 indium as internal standard. Optimal ablation was achieved with 50 pulses (microdroplets) and 20 pulses (plant tissues), using a 20 × 20 μm² beam, 0.25 J cm^-2 energy density, and 92 μs integration time. Transport efficiency ranged from 95-105%, calculated by comparing the single-particle events detected by LA-spICP-ToFMS with the number of particles estimated from a bulk analysis of the gelatin standards. As proof of concept, cotyledon and stem cross-sections from Phaseolus vulgaris bean sprouts grown in 30 nm AuNPs-supplemented aqueous medium (1 ppm Au) were analyzed. This approach enabled spatial mapping of AuNPs in terms of counts and particle number concentration, alongside quantitative maps of essential elements, demonstrating its suitability for investigating AuNPs uptake, translocation, and their effects on essential element distribution.