Colorimetric Assay for Determination of Lead (II) Based on Its Incorporation into Gold Nanoparticles during Their Synthesis

In this report, we present a new method for visual detection of Pb2+. Gold nanoparticles (Au-NPs) were synthesized in one step at room temperature, using gallic acid (GA) as reducer and stabilizer. Pb2+ is added during the gold nanoparticle formation. Analysis of Pb2+ is conducted by a dual strategy, namely, colorimetry and spectrometry. During Au-NPs synthesis, addition of Pb2+ would lead to formation of Pb-GA complex, which can induce the aggregation of newly-formed small unstable gold nanoclusters. Consequently, colorimetric detection of trace Pb2+ can be realized. As the Pb2+ concentration increases, the color turns from red-wine to purple, and finally blue. This method offers a sensitive linear correlation between the shift of the absorption band (Δλ) and logarithm of Pb2+ concentration ranging from 5.0 × 10−8 to 1.0 × 10−6 M with a linear fit coefficient of 0.998, and a high selectivity for Pb2+ detection with a low detection limit down to 2.5 × 10−8 M

Colorimetric Assay for Determination of Lead (II) Based on Its Incorporation into Gold Nanoparticles during Their Synthesis

In this report, we present a new method for visual detection of Pb2+. Gold nanoparticles (Au-NPs) were synthesized in one step at room temperature, using gallic acid (GA) as reducer and stabilizer. Pb2+ is added during the gold nanoparticle formation. Analysis of Pb2+ is conducted by a dual strategy, namely, colorimetry and spectrometry. During Au-NPs synthesis, addition of Pb2+ would lead to formation of Pb-GA complex, which can induce the aggregation of newly-formed small unstable gold nanoclusters. Consequently, colorimetric detection of trace Pb2+ can be realized. As the Pb2+ concentration increases, the color turns from red-wine to purple, and finally blue. This method offers a sensitive linear correlation between the shift of the absorption band (Δλ) and logarithm of Pb2+ concentration ranging from 5.0 × 10−8 to 1.0 × 10−6 M with a linear fit coefficient of 0.998, and a high selectivity for Pb2+ detection with a low detection limit down to 2.5 × 10−8 M

Validación de un método colorimétrico basado en nanopartículas de oro para la determinación de plomo (Pb+2) en muestras de agua para uso y consumo humano

El plomo (Pb+2) es un contaminante ambiental de alto riesgo para la salud. La OMS establece un valor límite máximo permisible de plomo en el agua potable de 48.3 nM. En contraposición, la Autoridad Europea de Seguridad Alimentaria (EFSA) describe efectos nocivos en el desarrollo neurológico a niveles de 10.1 nM de plomo en agua para el consumo humano. En la industria de los laboratorios analíticos, la cuantificación de Pb+2 en agua para uso y consumo humano está dominada por métodos basados en AAS, ICP/MS y ICP/OES. Estas metodologías carecen de sensibilidad para los niveles de concentración descritos por la EFSA. La metodología propuesta se basa en un sensor químico a partir de nanopartículas de oro de 14 nm de diámetro funcionalizadas con ácido maleico, capaz de detectar y reconocer al Pb+2 en solución de manera específica y selectiva, mediante la alteración del plasmón de resonancia de superficie localizado de las nanopartículas de oro como señal analítica detectable mediante espectrofotometría UV-Vis. La calidad del agua puede ser controlada a través de la medición de contaminantes ambientales por métodos que deben pasar previamente por una validación metodológica para brindar confiabilidad en los resultados analíticos. Entonces, debe validarse el método evaluando el desempeño de la metodología y estimando la incertidumbre del resultado. La validación demuestra que el método es lineal en un rango de concentraciones de 2.30 a 100 nM de Pb+2 con un coeficiente de determinación (r2) de 0.9948. La estimación de los límites de detección y cuantificación son 0.70 nM y 2.30 nM respectivamente. El método es veraz, al obtener 101.0% de recuperación para niveles de Pb+2 de 10 nM. Los interferentes estudiados en este trabajo no son fuente de error para los límites máximos permisibles (LMP) para la matriz de agua de uso y consumo humano descritos por el Ministerio de Salud del Perú.Tesi

Development of novel biosensing and diagnostic platforms using nanoparticle complexes

Metal nanomaterials, such as gold nanoparticles (Au NPs), exhibit unique localised surface plasmon resonance, which can be exploited for probing biochemical and biophysical phenomena at the nanoscale and molecular level. Furthermore, the ability to control the synthesis and growth of such nanomaterials using organic and biomimetic molecules, such as nucleic acids and small molecules, facilitates deeper understanding of the interactions between biomolecules and nanomaterials. This thesis described the development of various highly sensitive and novel diagnostic platforms for detecting micro-RNA (miRNA), small molecule and protein biomarkers, by utilising the unique plasmonic properties of Au NPs, as well as modulating the morphology and size of various gold nanostructures. Au NP-conjugated nucleic acid probes, together with a poly(ethylene glycol)-functionalised microarray, enabled highly sensitive and multiplexed detection of miRNAs, conveniently under an optical microscope. Also, colorimetric detection of small molecules using the naked eye was achieved via the controlled growth of aptamer-functionalised Au NPs into various distinct nanostructures, which were dependent on aptamer–target interactions and aptamer-mediated NP growth. Lastly, the interactions between small molecules and Au seeds, and the effect on the size and aspect ratios of grown gold nanorods were investigated and elucidated. The size-modulating mechanism was further incorporated in an immunoassay for the sensitive detection of a protein biomarker, enabling its application in clinical diagnostics. The platforms developed in this thesis could serve as a basis for future development of new biosensing strategies that utilise plasmonic nanomaterials.Open Acces

Investigation of Key Parameters Affecting Ion-Capturing Abilities of Mixed-Ligand Protected Gold Nanoparticles

Over the past decades, there has been a dramatic change in the types and amounts of metal ions in the biosphere, since we have introduced huge amount of metal waste into our environment in the course of industrialization of our society. Most of the metal cations persist in ecological systems and in the food chain, exposing top-level predators. Therefore, there is a huge need to develop sensitive, cost-effective, portable, and rapid sensing systems for continuous monitoring of the metal ions in various aquatic environments. The introduction of gold nanoparticles to the field of metal ion sensing has offered extensive opportunities to the design of miniaturized sensors with improved selectivity, limit of detection, signal-to-noise ratio, and response time. The ability to tune nanoparticlesâ properties by simple chemical modifications of their core or ligand shell was one of the key for their early successes in this field. In particular, the surface of gold nanoparticles (AuNPs) can be decorated with a wide range of organic ligands, which enables their selective interaction with a specific metal ion. A previous study from our group demonstrated that mixed-ligand coated gold nanoparticles in specific size and ligand compositions ranges were able to capture metal cations selectively. The ultimate goal at this thesis was to develop an understanding of such mixed-ligand coated nanoparticlesâ binding to metal cations. To achieve this goal, the ion binding capability of mixed-ligand coated AuNPs were systematically studied for nanoparticles of different ligand shell composition, and core size of the nanoparticles. Our results revealed that the selectivity and the binding ability of the studied particles to the cation of interest (here Cd+2) is strongly influenced by the parameter studies. We also found that the molecular conformation of the ligands for the particles in dry state has an unexpected and significant effect on the binding. In order to summarize the results obtained, a phase diagram was constructed. Understanding the concept behind the selectivity of our AuNPs in terms of ligand-shell conformation, which highly depends on the ligand composition and the size of AuNPs will enable researchers to develop selective sensors for detection of various metal ions