Multipath colourimetric assay for copper(II) ions utilizing MarR functionalized gold nanoparticles

Visual Cu2+ Detection of Gold-Nanoparticle Probes and its Employment for Cu2+ Tracing in Circuit System

Highly sensitive, simple and reliable colorimetric probe for Cu²⁺-ion detection was visualized with the L-cysteine functionalized gold nanoparticle (LS-AuNP) probes. The pronounced sensing of Cu²⁺ with high selectivity was rapidly featured with obvious colour change that enabled to visually sense Cu²⁺ ions by naked eyes. By employing systemic investigations on crystallinities, elemental compositions, microstructures, surface features, light absorbance, zeta potentials and chemical states of LS-AuNP probes, the oxidation-triggered aggregation effect of LS-AuNP probes was envisioned. The results indicated that the mediation of Cu²⁺ oxidation coordinately caused the formation of disulfide cystine, rendering the removal of thiol group at AuNPs surfaces. These features reflected the visual colour change for the employment of tracing Cu²⁺ ions in a quantitative way.

Functionalization of gold nanoparticles by β-cyclodextrin as a probe for the detection of heavy metals in water and photocatalytic degradation of textile dye

Gold nanoparticles (AuNPs) and AuNPs functionalized by β-cyclodextrin (β-CD/AuNPs) were prepared successfully through chemical reduction method. The structural, morphological, optical, compositional and vibrational studies for the AuNPs and β-CD/AuNPs were carried out. Functionalization of AuNPs by β-CD was confirmed with FT-IR results. The UV-visible absorption spectra exhibit a red-shift with decreasing average particle size. This sustains the enhancement in surface area (SA) to volume (V) ratio that is one of the peculiar characteristics of nanoparticles. TEM results show that β-CD/AuNPs formed were monodispersed and self assembled. Also it shows a decrease in average particle size and improved distribution. The use of β-CD in the synthesis of AuNPs are revealed not only create uniform small sized nanoparticles but these water soluble nanoparticles have very good antibacterial action by inhibiting the growth of bacteria commonly found in water and sensing activity for sensing the concentration of toxic metals in water. The sensitivity of the system towards copper (Cu) concentration was found as 1.788/mM for β-CD/AuNPs and 1.333/mM for AuNPs. The photocatalytic action of the obtained nanoparticles increases with decreasing average particle size. The k_app value of this photocatalytic degradation of textile dyeing waste water in presence of AuNPs was 0.002/min and β-CD/AuNPs was 0.005/min. This is a non-toxic and eco-friendly approach.

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.

One-step synthesis of amine-functionalized fluorescent silicon nanoparticles for copper(II) ion detection

Amine-functionalized silicon nanoparticles (A-SiNPs) with intense green fluorescence and photostability are synthesized via a one-step, low-cost hydrothermal method under mild conditions using 3-aminopropyl triethoxysilane (APTES) as a silicon source and L-ascorbic acid (AA) as a reducing reagent. The amine-rich surface not only improves water dispersability and stability of the A-SiNPs but also offers a specific copper(II) ion (Cu²⁺) coordination capability. The as-prepared A-SiNPs can be directly employed for Cu²⁺ detection in "turn-off" mode, resulting from Cu²⁺ coordination-induced fluorescence quenching effect. Under optimal conditions, Cu²⁺ detection was accomplished with a linear range from 1 to 500 μM and a limit of detection (LOD) at 0.1 μM, which was much lower than the maximum level (~ 20 μM) of Cu²⁺ in drinking water permitted by the US Environmental Protection Agency (EPA). In addition, the A-SiNPs were successfully used to detect Cu²⁺ in spiked river water, demonstrating its good selectivity and potential application for analysis of surface water samples. Graphical abstract.

Biology of MarR family transcription factors and implications for targets of antibiotics against tuberculosis

The emergence of multidrug resistant (MDR) Mycobacterium tuberculosis strains and increased incidence of HIV coinfection fueled the difficulty in controlling tuberculosis (TB). MarR (multiple antibiotic resistance regulator) family transcription factors can regulate marRAB operon and are involved in resistance to multiple environmental stresses. We have summarized the structure, function, distribution, and regulation of the MarR family proteins, as well as their implications for novel targets for antibiotics, especially for tuberculosis.

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 detection of magnesium (II) ions using tryptophan functionalized gold nanoparticles

The functional nanoparticles with specific molecular probe appear to be a promising approach for developing colorimetric nanosensor. In this work, we have synthesized tryptophan capped gold nanoparticles (AuNPs) and used to establish colorimetric detection of magnesium (Mg²⁺). The colorimetric response of the AuNPs toward Mg²⁺ was noticed with naked eyes, and spectral changes were monitored by using UV-Vis spectrophotometer. The detection response was rapid (less than 1 min), with a detection limit (LOD) about 0.2 µmol L⁻¹. The proposed nanoprobe shows characteristic red-shift of the AuNPs at 620 nm and high selectivity for Mg²⁺ due to the binding affinity of the tryptophan with Mg²⁺. The real-time response of the UV-Vis spectrum was monitored at three different concentrations of Mg²⁺ (0.45, 0.50, and 0.55 µmol L⁻¹). The AuNPs probe was suitable to provide a molecular platform for selective coordination with Mg²⁺ over Ca²⁺ ions, thus it could be facile to establish a practically viable sensing system. Furthermore, experimental results were confirmed to exhibit excellent linear curve for urine and serum samples spiked with Mg²⁺. Thus, this nanosensor is practically useful for the detection of Mg²⁺, without using expensive instruments, enzymes and/or DNA molecules.