Green nanoparticles show forensic promise but remain stuck at proof of concept

Green-synthesized nanoparticles are attracting growing attention in forensic science, but a comprehensive new review concludes that most reported applications remain at the proof-of-concept stage and are not yet ready for routine use in accredited laboratories. The structured narrative review, published in the Egyptian Journal of Forensic Sciences, examined plant-, microbial-, algal-, and biomolecule-mediated synthesis of metal and metal-oxide nanoparticles and assessed how their properties influence forensic applications ranging from latent fingermark development to trace drug detection.

The review, which screened 1,093 database records and included 178 studies, evaluated nanoparticles for latent fingermark development, surface-enhanced Raman spectroscopy (SERS), surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS), gunshot-residue analysis, forensic toxicology, questioned-document examination, and biological-evidence processing. Its central finding is sobering: while laboratory demonstrations are plentiful, direct quantitative comparisons with established forensic methods remain limited, and most studies relied on fresh, laboratory-prepared samples rather than aged, contaminated, or realistic casework evidence.

Green synthesis uses biological materials such as plant extracts, bacteria, fungi, algae, enzymes, proteins, and polysaccharides to reduce and stabilize metal ions into nanoparticles. The approach emerged from early work in the 2000s, including intracellular silver-nanoparticle formation using the fungus Verticillium and gold-nanoparticle formation in living alfalfa, followed by rapid extracellular synthesis of silver and gold nanoparticles using neem leaf extract. Conventional synthesis protocols, by contrast, may involve hazardous reducing agents, organic solvents, energy-intensive conditions, and surface contaminants that can affect both environmental sustainability and analytical compatibility.

However, the review stresses that the term “green” should not automatically be interpreted as non-toxic, inexpensive, or environmentally superior. Biological extracts contain polyphenols, flavonoids, terpenoids, sugars, proteins, and other metabolites that may act as reducing or stabilizing agents, but their composition varies with species, geographical origin, season, developmental stage, extraction conditions, and storage. Consequently, nominally identical synthesis protocols may produce nanoparticles with different yields, particle sizes, morphologies, surface charges, and storage stabilities, creating substantial batch-to-batch variation that directly affects analytical performance.

The review evaluates the complementary roles and limitations of the characterization techniques used to assess these materials. Ultraviolet-visible spectroscopy can monitor the formation of plasmonic nanoparticles such as silver and gold, but it cannot independently identify the reducing molecule or distinguish among nucleation, growth, and aggregation processes. Fourier-transform infrared spectroscopy provides indirect evidence of possible capping but does not prove that a particular functional group transferred electrons to the metal ion. X-ray diffraction confirms crystalline phase identity, while dynamic light scattering, zeta-potential analysis, electron microscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and Brunauer-Emmett-Teller surface-area analysis each contribute partial information. No individual technique is sufficient, and mechanistic conclusions require time-resolved measurements rather than colour change or endpoint characterization alone.

On the forensic applications side, the strongest comparative evidence concerns rice-husk-derived fingerprint powders. Rice-husk nanocarbon showed greater ridge selectivity than commercial black powder and achieved a higher mean score in a multiple-donor experiment, although the commercial powder performed better on several aged or depleted marks. In a quantitative comparison, rice-husk silica nanoparticles and commercial white powder produced statistically comparable fingermark grades across multiple donors and surfaces, and a subsequent study involving 36 donors, depletion series, and accelerated ageing similarly found comparable overall performance, with silica nanoparticles performing significantly better on selected surfaces including painted wood and soda bottles. These findings demonstrate that performance depends on the substrate, residue composition, and ageing conditions rather than the synthesis route alone.

Direct proof-of-concept evidence is also available for SALDI-MS, where plant-mediated silver nanoparticles were used to analyse latent fingermarks and detect endogenous fingermark constituents across the examined mass range. Yet even this study requires further investigation of detection limits, between-batch reproducibility, donor variability, ageing effects, and substrate interference before the method can support routine chemical profiling. Evidence for green nanoparticles in gunshot-residue analysis, questioned documents, toxicology, and DNA processing remains limited or largely prospective, and much of the available toxicology evidence concerns conventionally synthesized or surface-functionalized nanoparticles rather than green-synthesized ones.

The review also challenges common assumptions about sustainability and cost. Recent techno-economic analysis of colloidal silver production showed that a proprietary plant-extract process achieved a yield of approximately 75 percent at an estimated cost of USD 13,000 per kilogram and a global-warming potential of roughly 1,900 kg CO2-equivalent per kilogram, whereas green-tea-mediated synthesis produced a yield of only 1.13 percent at an estimated cost of USD 690,000 per kilogram and a global-warming potential of approximately 54,000 kg CO2-equivalent per kilogram. The sodium-borohydride route, by comparison, had an estimated global-warming potential of approximately 74,000 kg CO2-equivalent per kilogram. These process-specific values demonstrate that low yield and high precursor or energy consumption can negate the presumed benefits of a biological synthesis route, and that green synthesis does not make the final nanoparticle intrinsically non-toxic, since toxicity depends on composition, size, dose, surface chemistry, and residual contaminants.

For routine implementation in accredited forensic laboratories, the review sets out demanding requirements. A nanoparticle-based procedure would need documented validation consistent with ISO/IEC 17025, establishing sensitivity, selectivity, detection limits, precision, repeatability, reproducibility, robustness, matrix effects, and false-positive and false-negative rates. Batch-release testing should include nanoparticle yield, particle-size distribution, polydispersity index, zeta potential, morphology, crystallinity, surface chemistry, and storage stability, with acceptance limits established from repeated independent batches rather than universal thresholds. Evidence handling must preserve chain of custody, and laboratories must demonstrate that nanoparticle treatment does not compromise subsequent DNA profiling or other examinations on the same exhibit.

Looking ahead, the review identifies standardized extract characterization, batch-level quality control, storage-stability testing, real-sample validation, and interlaboratory reproducibility studies as essential priorities. Emerging tools may help: response-surface methodology and machine-learning approaches have been applied to optimize green-synthesized metal-oxide nanoparticles, and artificial intelligence could potentially predict particle size, yield, and colloidal stability from synthesis variables, although such applications to forensic-specific nanoparticles remain limited. Future opportunities include multifunctional nanoparticles combining fingermark visualization with chemical detection, portable SERS platforms, and smartphone-assisted imaging. Until paired studies compare green and conventional reagents using identical samples and report detection rates, examiner agreement, and cost per processed exhibit, the review concludes that green-synthesized nanoparticles should be regarded as promising complementary reagents rather than validated replacements for conventional forensic methods.

Subject of Research: Green-synthesized nanoparticles for forensic science applications and translation challenges

Article Title: Green-synthesized nanoparticles for forensic science: synthesis control, analytical validation, applications, and translation challenges

Article References: Thakur, S., Kumar, V., & Akhani, T. (2026). Green-synthesized nanoparticles for forensic science: synthesis control, analytical validation, applications, and translation challenges. Egyptian Journal of Forensic Sciences, 16(1), Article 90. https://doi.org/10.1186/s41935-026-00587-w

Image Credits: AI Generated

DOI: 10.1186/s41935-026-00587-w

Keywords: green synthesis, nanoparticles, forensic science, latent fingermarks, SERS, SALDI-MS, gunshot residue, batch variability, quality control, life-cycle assessment, ISO/IEC 17025, validation