The motivation behind the study is pressing. Neonicotinoids are among the most widely used insecticides on the planet, and nitenpyram, a first-generation member of the family, is applied extensively in both agriculture and veterinary medicine. Because the compound dissolves readily in water and resists biodegradation, it migrates easily into surface water and groundwater. The researchers cite evidence that as much as 80 to 90 percent of neonicotinoids applied in agricultural settings eventually reach aquatic systems, where they can accumulate and harm non-target organisms such as pollinators and aquatic invertebrates. Residues have been detected in surface waters, private wells, and even bottled water, raising concerns about human exposure through drinking water and the food chain. Effective, rapid monitoring of these contaminants is therefore a genuine public health need rather than an academic exercise.

Conventional analytical techniques such as gas chromatography, high-performance liquid chromatography, and chromatography coupled with mass spectrometry can certainly detect neonicotinoids with excellent sensitivity and selectivity. But they demand expensive instrumentation, complicated sample preparation, lengthy analysis times, and highly trained operators, all of which limit their usefulness for rapid, on-site screening of environmental samples. Nanomaterial-based sensing platforms have emerged as attractive alternatives because they respond quickly, are operationally simple, and can be exquisitely sensitive. Among fluorescent nanomaterials, silicon nanoparticles stand out for their low cytotoxicity, strong photostability, tunable optical properties, and easy surface functionalization. The catch has been that many reported synthesis routes rely on high-temperature processes, hazardous reagents, and energy-intensive conditions that sit awkwardly with the principles of green chemistry.

The Chinese team’s solution was to replace the commercial reducing agent with one harvested from waste. Fresh pineapple peels were washed, cut, and homogenized in cold 3 percent metaphosphoric acid, which stabilizes ascorbic acid and prevents its oxidation during extraction. The ascorbic acid content of the peels was then quantified by iodometric titration, a classical analytical technique that exploits the one-to-one reaction between iodine and vitamin C. The measurement revealed 95.08 milligrams of ascorbic acid per 100 grams of fresh peel, and the clarified extract registered a pH of 3.54, confirming its acidic character. By quantifying the reducing capacity of the extract before synthesis, the researchers reduced the uncertainty that naturally arises when a variable biological feedstock replaces a standardized laboratory reagent.

The synthesis itself is strikingly simple. Twenty milliliters of the pineapple peel extract were stirred at room temperature while two milliliters of the silane precursor AEEA, or N-(2-aminoethyl)-2-aminoethanol silane, were added dropwise. Over seven hours at ambient temperature, the solution gradually developed a bright yellow color, signaling the formation of fluorescent nanoparticles, which the team calls P-SiNPs. The suspension was filtered through a 0.22 micrometer syringe filter, purified by dialysis against a 3000 dalton membrane, and stored at 4 degrees Celsius. Control experiments confirmed that neither the extract nor the silane alone produced fluorescence; only when the two were combined did the characteristic emission appear, centered near 480 nanometers. Batches prepared from independently extracted peel lots showed comparable fluorescence intensities, emission maxima, and absorption profiles, an early indication that the biomass route can be reproducible.

Structural characterization painted a detailed picture of the new nanoprobes. Transmission electron microscopy revealed well-dispersed, uniform spherical particles with an average diameter of roughly 1.69 nanometers, small enough to qualify as among the tiniest fluorescent silicon nanoparticles reported. Energy-dispersive X-ray spectroscopy and elemental mapping showed homogeneous distributions of silicon, carbon, nitrogen, and oxygen throughout the particles. X-ray photoelectron spectroscopy quantified the composition at approximately 4 percent silicon, 37 percent carbon, 20 percent nitrogen, and 34 percent oxygen, with high-resolution spectra revealing silicon bonded to carbon, nitrogen, and oxygen. The team calculated a photoluminescence quantum yield of 2.11 percent, which they note compares favorably with other published silicon nanoparticles. The abundance of hydroxyl, amino, and siloxane-related surface groups, they argue, underpins both the particles’ water dispersibility and their ability to recognize nitenpyram.

When nitenpyram was introduced, the nanoparticles responded in two complementary ways. Their green fluorescence at 480 nanometers, excited at 350 nanometers, was progressively quenched as insecticide concentration increased, while their ultraviolet-visible absorption spectrum was simultaneously enhanced. The fluorescence response was linear from 0 to 165 micromolar, fitting a Stern-Volmer equation with a correlation coefficient of 0.988, and the detection limit came out at 0.028 micromolar. The colorimetric channel proved even more sensitive, with a detection limit of 0.0018 micromolar and a linear range spanning the same concentration window. Both limits are lower than those reported in previous nitenpyram sensing studies, according to the authors’ comparison with the literature, underscoring the analytical power of combining two independent optical readouts in a single probe.

Unraveling the quenching mechanism required an arsenal of spectroscopic tools. The absorption spectrum of nitenpyram overlapped negligibly with the excitation and emission spectra of the nanoparticles, ruling out Förster resonance energy transfer and the inner filter effect as dominant causes. Temperature-dependent Stern-Volmer analysis at 298, 313, and 323 kelvin showed quenching constants that decreased slightly as temperature rose, a hallmark of static quenching in which a ground-state complex forms between the fluorophore and the quencher. The calculated bimolecular quenching rate constants, on the order of 10 to the 11th to 10 to the 12th liters per mole per second, far exceed the diffusion-controlled limit of about 2.0 times 10 to the 10th, further arguing against simple collisional quenching. Time-resolved fluorescence added another clue: the average lifetime lengthened from 4.93 nanoseconds to 7.003 nanoseconds upon nitenpyram binding, indicating that the insecticide alters the photophysical relaxation pathways of the emissive surface states.

The structural evidence was equally telling. After exposure to nitenpyram, the apparent particle size measured by transmission electron microscopy dropped from 1.69 nanometers to about 0.55 nanometers, and lattice-like fringes with a spacing of 0.554 nanometers appeared in the images, accompanied by a broadened diffraction peak in the X-ray diffraction pattern. Infrared spectroscopy showed changes in the regions associated with hydroxyl and amino groups as well as the pyridine skeleton vibrations characteristic of nitenpyram, while zeta-potential measurements recorded a shift from 1.33 millivolts to negative values after insecticide addition, a charge reversal consistent with nitenpyram associating at the nanoparticle-water interface. The authors interpret this constellation of observations as a quenching mechanism dominated by complexation-triggered structural reconstruction at the functionalized surface, which suppresses surface-defect emission and accelerates non-radiative energy dissipation. They are careful to acknowledge that because the evidence is spectroscopic and ensemble-averaged, the precise binding geometry and the relative contributions of hydrogen bonding, donor-acceptor interactions, and surface-state reconstruction cannot yet be conclusively resolved.

Practical performance sealed the case. The nanoparticles kept their fluorescence nearly constant from 25 to 100 degrees Celsius, remained stable for more than eight hours at room temperature, tolerated 100 millimolar sodium chloride, and responded predictably across pH conditions. Selectivity tests against structurally related neonicotinoids such as imidacloprid and acetamiprid, along with a panel of metal ions, anions, humic acid, and aromatic compounds, showed that only nitenpyram triggered a marked optical response, even when interferents were present at three times its concentration. The researchers attribute this discrimination to the electron-deficient nitro group and heteroaromatic structure of nitenpyram, which can engage the electron-rich amine and silanol surface sites through hydrogen bonding, electrostatic attraction, and charge-transfer interactions. When the platform was applied to real water from a fishing pond, an irrigation pond, a tributary of the Maozhou River near agricultural land, and a campus lake at Sun Yat-sen University, spiked-recovery tests yielded fluorometric recoveries of 99.00 to 101.45 percent and colorimetric recoveries of 95.71 to 104.30 percent, with relative standard deviations below 3.5 and 2.5 percent respectively. Beyond the analytical numbers, the study sketches a circular chemistry strategy: a reagent that would otherwise cost roughly 70 dollars per kilogram is replaced by fruit waste, synthesis proceeds without heating, and the resulting sensor helps safeguard the very water systems that agricultural runoff threatens.

Subject of Research: Green synthesis of fluorescent silicon nanoparticles from pineapple peel waste for dual-mode detection of the neonicotinoid insecticide nitenpyram in environmental water

Article Title: Pineapple peel-derived ascorbic acid-assisted green synthesis of fluorescent silicon nanoparticles for dual-mode monitoring of nitenpyram

Article References: Iradukunda, Y., Zhang, F., Xin, X., Yang, J., Li, L., Habumugisha, T., & Yan, W. (2026). Pineapple peel-derived ascorbic acid-assisted green synthesis of fluorescent silicon nanoparticles for dual-mode monitoring of nitenpyram. Results in Engineering, 32, Article 113320. https://doi.org/10.1016/j.rineng.2026.113320

Image Credits: AI Generated

DOI: 10.1016/j.rineng.2026.113320

Keywords: silicon nanoparticles, pineapple peel waste, ascorbic acid, green synthesis, nitenpyram, neonicotinoid insecticides, fluorescence quenching, water monitoring, dual-mode sensing, environmental chemistry, nanosensors, agricultural runoff

The analytical backbone of the study was a modified QuEChERS extraction procedure coupled with ultra-high performance liquid chromatography tandem mass spectrometry, a combination that allows trace-level quantification of multiple pesticide residues across chemically distinct matrices. This approach matters because herbicides behave very differently depending on where they end up. Some dissolve readily into water and travel with runoff; others bind to soil particles and hitch a ride on eroded sediment. By sampling soil, sediment, and water simultaneously and repeatedly across wet, dry, and transitional seasons, the team could trace those partitioning behaviors in a real watershed rather than inferring them from laboratory models alone.

One compound dominated the picture: diuron. This phenylurea herbicide, widely used to control weeds in orchards and cane fields, was detected frequently, with soil concentrations ranging from 0.309 to 175.406 micrograms per kilogram and sediment values reaching 91.292 micrograms per kilogram. Diuron’s persistence is well documented in other systems; it degrades slowly, adsorbs to organic matter, and can linger long after application. Its prominence in both soil and sediment of the Nala watershed suggests a reservoir of legacy and ongoing inputs that continues to feed the aquatic system, even between spraying seasons.

In the water column itself, the headline compounds were different. Ametryn, a triazine herbicide used heavily in sugarcane cultivation, reached a maximum concentration of 30.294 micrograms per liter in surface water, while mesotrione, a triketone herbicide, peaked at 20.264 micrograms per liter. These are striking figures for ambient surface waters, and they reflect the intensity of herbicide use in a watershed where sugarcane and other subtropical crops receive multiple applications per growing cycle. The fact that the dominant compounds shift between matrices underscores a central theme of the study: there is no single herbicide problem, but rather a suite of compound-specific contamination patterns.

The seasonal dynamics proved equally revealing, and somewhat counterintuitive. In soil, the predominant herbicides, particularly diuron and ametryn, showed significantly elevated concentrations in spring, which aligns neatly with pre-planting and early-season weed control. Yet in sediment, the predominant herbicides displayed no significant seasonal differences at all, hinting at a buffered, slowly exchanging pool that accumulates residues over time. Surface water told a third story: several compounds varied significantly across seasons, but the patterns diverged by compound. Butachlor, a chloroacetanilide used in paddy and wetland systems, reached its highest median concentration in summer, while ametryn and mesotrione showed their numerical maxima in spring.

Those contrasting temporal signatures allowed the researchers to disentangle two forces that shape pesticide fate in agricultural catchments. Application timing clearly controls the initial pulse of herbicides entering the environment, which explains the spring peaks in soil and in compounds applied early in the season. But once residues are mobilized, rainfall and hydrological processes take over, governing transport, redistribution, and dilution across the watershed. The summer peak of butachlor, a compound associated with flooded rice systems, likely reflects both its use pattern and the intense monsoon-season runoff that flushes it from fields into streams. In effect, the watershed integrates a chemical calendar written by farmers with a hydrological calendar written by the climate.

Space mattered as much as time. Higher residue levels clustered primarily in the southwestern agricultural areas of the watershed, where cultivation intensity is greatest, while downstream redistribution became evident during the rainy season as runoff carried dissolved and particle-bound herbicides toward lower reaches. This spatial structure has practical implications: it identifies hotspot zones where mitigation efforts, such as vegetated buffer strips, controlled drainage, or adjusted application schedules, would deliver the greatest reduction in downstream loading. It also demonstrates that a watershed cannot be managed as a uniform unit; pollution pathways are dictated by the geography of farming and the connectivity of the drainage network.

The ecological risk assessment is where the study’s findings become most alarming. Using the risk quotient approach, which compares measured environmental concentrations to toxicity thresholds for aquatic organisms, the team identified diuron, ametryn, and imazapic as the principal risk drivers in surface water. Maximum risk quotients reached 1251.23 for diuron, 841.50 for ametryn, and 789.20 for imazapic, values that are orders of magnitude above the threshold of 1 typically used to flag unacceptable risk. More concerning still, the median risk quotients for these three compounds remained above 1, meaning that at typical, not just extreme, concentrations, the water poses sustained ecological concern throughout much of the year.

The risk landscape beyond the top three drivers was more nuanced. Several additional herbicides also exhibited median risk quotients greater than 1, though at lower magnitudes, indicating chronic pressure from a broader suite of compounds. Others showed high maximum risk quotients but lower medians, a pattern the authors interpret as episodic risk, where brief pulses after rainfall or application events push concentrations past toxic thresholds even if average levels appear tolerable. Episodic exposure is ecologically significant because aquatic communities often respond to peak concentrations, and short pulses during sensitive life stages, such as larval development, can cause disproportionate harm. A monitoring program that samples infrequently would miss exactly these events, which is why the monthly resolution of this study is methodologically important.

What emerges from the Nala watershed is a systems-level insight: herbicide occurrence, transport, and ecological risk in subtropical agricultural regions are jointly governed by agricultural practices, compound-specific environmental behavior, and hydrological processes. None of these factors can be addressed in isolation. The authors position their work as a scientific basis for targeted herbicide monitoring, runoff control, and watershed-based pollution management, and the data support concrete interventions, from timing applications to avoid pre-monsoon windows to prioritizing the southwestern hotspot zones for best-management practices. As herbicide use intensifies across the subtropical belt to feed growing populations, studies like this one provide the evidence base needed to keep crop protection from becoming waterway contamination, and they make clear that in intensively farmed watersheds, the two are currently separated by a very thin line.

Subject of Research: Occurrence, seasonal and spatial distribution, and aquatic ecological risk of sixteen current-use herbicides in a subtropical agricultural watershed in South China

Article Title: Occurrence, spatiotemporal distribution, and risk assessment of herbicides in a subtropical agricultural watershed

Article References: Liu, L., Mo, G., Zhao, Y., Rasheed, U., Li, Y., Hu, M., Qin, Q., Qin, Y., Tan, H., & Shan, B. (2026). Occurrence, spatiotemporal distribution, and risk assessment of herbicides in a subtropical agricultural watershed. Environmental Monitoring and Assessment, 198(10), Article 1094. https://doi.org/10.1007/s10661-026-15948-0

Image Credits: AI Generated

DOI: 10.1007/s10661-026-15948-0

Keywords: herbicides, diuron, ametryn, imazapic, butachlor, mesotrione, agricultural runoff, watershed, ecological risk assessment, risk quotient, surface water contamination, subtropical agriculture