Self-assembled gold nanoparticles and amphiphile peptides: a colorimetric probe for copper(ii) ion detection

We show that arginine/phenylalanine based peptides can be used to control the aggregation of gold nanoparticles in different ways. The arrangement provides a colorimetric approach to detect Cu²⁺ ions in water.

Integrated optical and electrochemical detection of Cu2+ ions in water using a sandwich amino acid–gold nanoparticle-based nano-biosensor consisting of a transparent-conductive platform

In this paper, an optical-electrochemical nano-biosensor was introduced for measuring Cu²⁺ ion concentrations in water. A multi-step procedure was used to fabricate the transparent-conductive biosensor platform consisting of an l-cysteine–gold nanoparticle-based sandwich structure. First, colloidal gold nanoparticles (GNPs) were synthesized according to the Turkevich–Frens method with some modifications and then functionalized with l-cysteine molecules (GNP/l-cys). Then, cyclic voltammetry was preformed in buffered solutions containing HAuCl₄·3H₂O for gold nanoparticle electrodeposition on cleaned ITO glasses. The GNP-electrodeposited ITO glasses (ITO/GNPs) were thermally treated in air atmosphere for 1 hour at a temperature of 300 °C. Following the procedure, the gold nanoparticles on ITO/GNPs substrates were functionalized with l-cysteine to prepare ITO/GNPs/l-cys substrates. Finally, the sandwich-type substrates of ITO/GNPs/l-cys⋯Cu²⁺⋯l-cys/GNPs were fabricated by accumulation of Cu²⁺ ions using an open circuit technique performed in copper ion buffer solutions in the presence of previously produced colloidal GNP/l-cys nanoparticles. The effective parameters including GNP/l-cys solution volume, pre-concentration pH and pre-concentration time on the LSPR and SWV responses were investigated and optimized. The fabricated transparent-conductive platforms were successfully assessed as a nano-biosensor for detection of copper ions using two different methods of square wave voltammetry (SWV) and localized surface plasmon resonance (LSPR). As a result, the proposed biosensor showed a high sensitivity, selectivity and a wide detectable concentration range to copper ions. The total linear range and the limit of detection (LOD) of the nano-biosensor were 10–100 000 nM (0.6–6354.6 ppb) and below 5 nM (0.3 ppb), respectively. The results demonstrated the potential of combining two different optical and electrochemical methods for quantitation of the single analyte on the same biosensor platform and obtaining richer data. Also, these results indicated that the developed LSPR-SWV biosensor was superior to many other copper biosensors presented in the literature in terms of linear range and LOD. The developed nano-biosensor was successfully applied in the determination of trace Cu²⁺ concentration in actual tap water samples.

The transparent-conductive platforms of ITO/GNPs/l-cys⋯Cu²⁺⋯l-cys/GNPs were fabricated for quantitation of Cu²⁺ ions in water samples using combined LSPR and SWV methods.

Colorimetric detection of Cu2+ based on the formation of peptide-copper complexes on silver nanoparticle surfaces

We developed a colorimetric method for the rapid detection of copper ions (Cu²⁺) in aqueous solution. The detection of Cu²⁺ is based on coordination reactions of Cu²⁺ with casein peptide-functionalized silver nanoparticles (AgNPs), leading to a distinct color change of the solution from yellow to red. The developed method has a good detection limit of about 0.16 µM Cu²⁺ using 0.05 mL of AgNPs stock solution and a linearity in the range of 0.08-1.44 µM Cu²⁺ with a correlation coefficient of R² = 0.973. The developed method is a useful tool for the detection of Cu²⁺ ions. Furthermore, it can be used for monitoring Cu²⁺ in water at concentrations below the safe limit for drinking water set by the World Health Organization.

Colorimetric disposable paper coated with ZnO@ZnS core-shell nanoparticles for detection of copper ions in aqueous solutions

In this study, we have proposed a new nanoparticle-containing test paper sensor that could be used as an inexpensive, easy-to-use, portable, and highly selective sensor to detect Cu(2+) ions in aqueous solutions. This disposable paper sensor is based on ZnO@ZnS core-shell nanoparticles. The core-shell nanoparticles were synthesized using a chemical method and then they were used for coating the paper. The synthesis of the ZnO@ZnS core-shell nanoparticles was performed at a temperature as low as 60 °C, and so far this is the lowest temperature for the synthesis of such core-shell nanoparticles. The sensitivity of the paper sensor was investigated for different Cu(2+) ion concentrations in aqueous solutions and the results show a direct linear relation between the Cu(2+) ions concentration and the color intensity of the paper sensor with a visual detection limit as low as 15 μM (∼0.96 ppm). Testing the present paper sensor on real river turbulent water shows a maximum 5% relative error for determining the Cu(2+) ions concentration, which confirms that the presented paper sensor can successfully be used efficiently for detection in complex solutions with high selectivity. Photographs of the paper sensor taken using a regular digital camera were transferred to a computer and analyzed by ImageJ Photoshop software. This finding demonstrates the potential of the present disposable paper sensor for the development of a portable, accurate, and selective heavy metal detection technology.

Highly sensitive visual detection of copper (II) using water-soluble azide-functionalized gold nanoparticles and silver enhancement

A high-sensitive method for the visual detection of copper ions in aqueous solution is developed. The method is based on copper ion-catalyzed 'click' reaction between the water-soluble azide-functionalized gold nanoparticles (AuNPs) and alkyne-modified glass slide. The PEG linker was employed as a stabilizing component along with the terminal azide group to keep the AuNPs stably dispersed in water without the assistance of any organic solvent. In the presence of copper ions, the AuNPs are 'clicked' on the slide, and the darkness of the AuNPs in the sample spot is promoted by silver enhancement process. Only a tiny amount of sample (10 μl) is needed with the detectable concentration down to 62 pM by the commonly used flatbed scanner, which is 2-3 orders of magnitude lower than those in previous reports. The selectivity relative to other potentially interfering ions and the applicability in real samples, human serum and tap water, have also been evaluated. Our method has a good potential in point-of-use applications and environment surveys.

Sensing of biologically important cations such as Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) using magnetic nanoemulsions

We report a simple approach to the ultrasensitive detection of biologically important metal ions using a magnetic nanoemulsion. The nanoemulsion used in our study was an oil-in-water emulsion droplet of average size ∼190 nm containing ferrimagnetic iron oxide nanoparticles of average size ∼10 nm. In a static magnetic field, the emulsion droplets self-assemble into a nanoarray with distinct interdroplet spacing. In the presence of cations in the solution, the nanofluid array shows a large blue shift in the diffracted Bragg peak and a visually perceivable color change due to changes in the electrical double layer upon the diffusion of cations. The colloidal force-distance measurements in the presence of cations show large variations at the onset of repulsion in the presence of cations. The sensor shows good selectivity to Na(+), K(+), Ca(2+), Cu(2+), and Fe(3+) ions and offers a rapid response compared to conventional techniques. This approach can be useful for the recognition of biologically important cations.