Selective visual detection of Pb(II) ion via gold nanoparticles coated with a dithiocarbamate-modified 4′-aminobenzo-18-crown-6

An electrochemical sensor–adsorbent for lead (Pb2+) ions in an aqueous environment based on Katiragum–Arginine Schiff base

A dual functional material fulfilling twin objectives; simultaneous sensing and adsorption of Pb2+ ions in an aqueous medium.

Chemical sensing with Au and Ag nanoparticles

Noble metal nanoparticles (NPs) are ideal scaffolds for the fabrication of sensing devices because of their high surface-to-volume ratio combined with their unique optical and electrical properties which are extremely sensitive to changes in the environment. Such characteristics guarantee high sensitivity in sensing processes. Metal NPs can be decorated with ad hoc molecular building blocks which can act as receptors of specific analytes. By pursuing this strategy, and by taking full advantage of the specificity of supramolecular recognition events, highly selective sensing devices can be fabricated. Besides, noble metal NPs can also be a pivotal element for the fabrication of chemical nose/tongue sensors to target complex mixtures of analytes. This review highlights the most enlightening strategies developed during the last decade, towards the fabrication of chemical sensors with either optical or electrical readout combining high sensitivity and selectivity, along with fast response and full reversibility, with special attention to approaches that enable efficient environmental and health monitoring.

Limitations for colorimetric aggregation assay of metal ions and ways of their overcoming

The development of analytical methods for the determination of metal ions in water is one of the priority tasks for efficient environmental monitoring. The use of modified gold nanoparticles and the colorimetric detection of their aggregation initiated by ions binding with specific receptors on the nanoparticle surface has high potential for simple testing. However, the limits of this approach and the parameters determining the assay sensitivity are not clear, and the possibilities of different assay formats are estimated only empirically. We have proposed a mathematical description of the aggregation processes in the assay and have estimated the detection limits of an aptamer-based assay of Pb2+ ions theoretically and experimentally. In the studied assay, gold nanoparticles modified with G,T-enriched aptamer were used, and their aggregation caused by the interaction with Pb2+ ions was controlled via a color change. The experimentally determined limit of Pb2+ detection was 700 ppb, which was in good agreement with theoretical calculations. An examination of the model showed that the limiting parameter of the assay is the binding constant of the aptamer-Pb2+ ion interaction. To overcome this limitation without searching for alternate receptors, two methods have been proposed, namely additional aggregation-causing components or centrifugation. These approaches lowered the detection limit to 150 ppb and even to 0.4 ppb. The second value accords with regulatory demands for the permissible levels of water source contamination, and the corresponding approach has significant competitive potential due to its rapidity, simple implementation, and the visual assessment of the assay results.

Further Approaches in the Design of Antitumor Agents with Response to Cell Resistance: Looking toward Aza Crown Ether-dtc Complexes

The dianionic aza crown ether-dtc N,N'-bis(dithiocarbamate)-1,10-diaza-18-crown-6 (L^2-) is a versatile ligand capable of yielding binuclear complexes with group 10 elements, also known as Ni-triade, [μ-(κ²-S,-S'-L)M₂(PPh₃)₄]Cl₂ (M = Pd (1), Pt (2)), [μ-(κ²-S,-S'-L)M₂(PPh₃)₄](BPh₄)₂ (M = Pd (3), Pt (4)), and μ-(κ-S,-S'-L)Ni₂(PPh₃)₂Cl₂ (5), and has proven to be an excellent option to the design of metal-based drugs able to provide multiple response to cell resistance. Palladium and platinum complexes, 1 and 2, were tested for cytotoxicity in the human cervix carcinoma cell line HeLa-229, the human ovarian carcinoma cell line A2780, and the cisplatin-resistant mutant A2780cis, finding significant activity toward all three cancer cell lines, with low micromolar IC₅₀ values, comparable to cisplatin. Markedly, against the cisplatin resistant cell line A2780cis, compound 2 exhibits better cytotoxic activity than the clinical drug (IC₅₀ = 2.3 ± 0.2 μM for 2 versus 3.6 ± 0.5 μM for cisplatin). Moreover, an enhancement of the antitumor response is achieved when adding an equimolar amount of alkali metal chloride (NaCl or KCl) to the medium, for instance, testing compound 1 against the cisplatin-resistant A2780cis cells, the IC₅₀ decreases from 9.3 ± 0.4 to 7.4 ± 0.3 and 5.4 ± 0.1 μM, respectively, after addition of the salt solution. For the platinum derivative 2, the IC₅₀ improves by ca. 40% reaching 1.3 ± 0.1 μM when potassium chloride is added. Likewise, the resistant factor found for 2 (RF = 1) confirms that this complex circumvents cisplatin-resistance in A2780cis and is improved with the addition of potassium chloride (RF = 0.65). The presence of the aza crown ether moiety as linker in the systems studied herein is a key point since, in addition to allowing and facilitating interaction with alkali metal ions, this unit is flexible enough to adapt to a variety of environments, as confirmed by the X-ray crystal structures described, where different conformations and ways to fold in are found. In order to gain insight into the electronic and structural facts involved in the interaction of complex 2 with the alkali metal ions, a DFT study was performed, and the description of the molecular electrostatic potentials (MEPs) is also presented.

Assembly of 6-aza-2-thiothymine on gold nanoparticles for selective and sensitive colorimetric detection of pencycuron in water and food samples

A facile and novel nanosensor analytical strategy was developed for the colorimetric detection of pencycuron fungicide in rice, potato, cabbage, and water samples based on the pencycuron-induced aggregation of 6-aza-2-thiothymine-functionalized gold nanoparticles (ATT-AuNPs). The ATT-AuNPs exhibited good stability and were characterized with UV-visible spectroscopy, Fourier transform infrared (FT-IR) spectrometry, field-emission scanning electron microscopy (FE-SEM), transmission electron microscopy (TEM), dynamic light scattering (DLS), and zeta potential techniques. The addition of pencycuron facilitated strong non-covalent interactions (electrostatic, van der Waals, and H bonding) between pencycuron and ATT-AuNPs, inducing a significant red shift in the surface plasmon resonance (SPR) peak of ATT-AuNPs along with a color change from red to blue. A linear equation was established between absorption ratio (A₇₂₀/A₅₂₈) and pencycuron concentration (2.5-100 μM) with a correlation coefficient (R²) of 0.9915. The detection limit was calculated to be 0.42 μM, which was much lower than that of other analytical methods. The designed ATT-AuNP serves as a promising nanosensor for the rapid, simple, and selective label-free colorimetric detection of pencycuron in rice, potato, cabbage, and water samples, is highly sensitive, and does not require sophisticated instruments, tedious sample preparations, and time-consuming separation and pre-concentration procedures.

Facile conversion of kaolinite into clay nanotubes (KNTs) of enhanced adsorption properties for toxic heavy metals (Zn2+, Cd2+, Pb2+, and Cr6+) from water

Kaolinite nanotubes (KNTs) were synthesized from kaolinite by ultrasonic scrolling and characterized using X-ray diffractometer, scanning and transmission electron microscopes; and FTIR-FT Raman spectrometer. The synthetic KNTs appear as multi-walled scrolls of 12 nm average pore diameter and 50-600 nm particle length; and exhibit surface area of 105 m²/g. KNTs were used as adsorbents for Zn²⁺, Cd²⁺, Pb²⁺, and Cr⁶⁺ with uptake capacities of 103 mg/g, 116 mg/g, 89 mg/g, and 91 mg/g, respectively. The equilibration time of Cd²⁺ and Pb²⁺ adsorption is 360 min and for Cr⁶⁺ and Zn²⁺ area 120 min and 240 min, respectively. KNTs adsorption systems can be described mainly by Lagergren-second order and Freundlich models (R²> 0.95) as kinetic and isotherm models. This reflected multilayer adsorption forms with chemical sharing or ion exchange processes. KNTs exhibits high reusability and used for five cycles in the removal of the studied metals (100 mg/L). The removal percentages declined by 20.5%, 15.12%, 22.8% and 23.16% with repeating the reused cycles from cycle 1 to cycle 5 for Zn²⁺, Cd²⁺, Pb²⁺, and Cr⁶⁺, respectively. KNTs were applied successfully in realistic purification of tap water, groundwater, and sewage water from the inspected metals.

Design of Lanthanide-Doped Colloidal Nanocrystals: Applications as Phosphors, Sensors, and Photocatalysts

The unique optical characteristics of lanthanides (Ln³⁺) such as high color purity, long excited-state lifetimes, less perturbation of excited states by the crystal field environment, and the easy spectral conversion of wavelengths through upconversion and downconversion processes have caught the attention of many scientists in the recent past. To broaden the scope of using these properties, it is important to make suitable Ln³⁺-doped materials, particularly in colloidal forms. In this feature article, we discuss the different synthesis strategies for making Ln³⁺-doped nanoparticles in colloidal forms, particularly ways of functionalizing hydrophobic surfaces to hydrophilic surfaces to enhance their dispersibility and luminescence in aqueous media. We have enumerated the various strategies and sensitizers utilized to increase the luminescence of the nanoparticles. Furthermore, the use of these colloidal nanoparticle systems in sensing application by the appropriate selection of capping ligands has been discussed. In addition, we have shown how the energy transfer efficiency from Ce³⁺ to Ln³⁺ ions can be utilized for the detection of toxic metal ions and small molecules. Finally, we discuss examples where the spectral conversion ability of these materials has been used in photocatalysis and solar cell applications.

Resonance light scattering sensor of the metal complex nanoparticles using diethyl dithiocarbamate doped graphene quantum dots for highly Pb(II)-sensitive detection in water sample

This study was aimed to detect Pb²⁺ using diethyl dithiocarbamate-doped graphene quantum dots (DDTC-GQDs) based pyrolysis of citric acid. The excitation maximum wavelength (λ_max, ex = 337 nm) of the DDTC-GQDs solution was blue shift from bare GQDs (λ_max, ex = 365 nm), with the same emission maximum wavelength (λ_max, em = 459 nm) indicating differences in the desired N, S matrices decorating in the nanoparticles. Their resonance light scattering intensities were peaked at the same λ_max, ex/em = 551/553 nm without any background effect of both ionic strength and masking agent. Under optimal conditions, the linear range was 1.0-10.0 μg L^-1 (R² = 0.9899), limit of detection was 0.8 μg L^-1 and limit of quantification was 1.5 μg L^-1. The precision, expressed as the relative standard deviations, for intra-day and inter-day analyses was 0.87% and 4.47%, respectively. The recovery study of Pb²⁺ for real water samples was ranged between 80.8% and 109.5%. The proposed method was also proved with certified water sample containing 60 μg L^-1 Pb²⁺ giving an excellent accuracy and was then implied satisfactorily for ultra-trace determination of Pb²⁺ in drinking water and tap water samples.

Superior removal of Co2+, Cu2+ and Zn2+ contaminants from water utilizing spongy Ni/Fe carbonate-fluorapatite; preparation, application and mechanism

Spongy Ni/Fe carbonate - fluorapatite was synthesized from natural phosphorite enriched with iron impurities. The morphological, chemical and structural features of the product were estimated using several techniques as XRD, SEM, EDX, and FT-IR. It exhibits spongy structure of nano and micro-pores. The average crystallite size is about 8.27 nm. The suitability of the product for considerable decontamination of Zn²⁺, Co²⁺, and Cu²⁺, ions from water was studied based on several reacting parameters. The equilibrium was attained after 240 min for Zn²⁺ and Co²⁺ ions while the adsorption equilibrium of Cu²⁺ reached after 120 min. The adsorption data for the selected metals was represented well by a pseudo-second-order model which revealed chemisorption uptake. The equilibrium studies were appraised based on traditional models and two advanced models were designed according to the statistical physical theories. The adsorption results highly fitted with Langmuir model followed rather than the other models. This indicated a monolayer adsorption for the metal ions by spongy Ni/Fe carbonate - fluorapatite. The estimated q_max values are 149.25 mg/g, 106.4 mg/g and 147.5 mg/g for the uptake of Zn²⁺, Co²⁺, and Cu²⁺, respectively. Based on monolayer models of one energy and two energies, the number of receptor adsorption sites, number of adsorbed metal ions per active site, the average number of sites which occupied by ions, mono layer adsorption quantity and the adsorption quantity after total saturation were calculated for the first time for such materials.

An electrochemical biosensor for the detection of Pb2+ based on G-quadruplex DNA and gold nanoparticles

We present a novel simple strategy for the detection of Pb²⁺ based on G-quadruplex DNA and gold nanoparticles. First, gold nanoparticles were chemically adsorbed onto the surface of a thiol-modified gold electrode. Subsequently, the substrate DNA1 was adsorbed onto the surfaces of the gold nanoparticles via thiol-gold bonds, so that the complementary guanine-rich DNA2 could be hybridized to the gold electrode in sequence. [Ru(NH₃)₆]³⁺ (RuHex), which can be electrostatically adsorbed onto the anionic phosphate of DNA, served as an electrochemical probe. The presence of Pb²⁺ can induce DNA2 to form a stable G-quadruplex and fall off the gold electrode. The amount of RuHex remaining on the electrode surface was determined by electrochemical chronocoulometry (CC). The prepared biosensor showed high sensitivity for Pb²⁺ with a linear range with respect to ln(c_Pb2+) from 0.01 to 200 nM and a low detection limit of 0.0042 nM under optimal conditions. Because of the high selectivity of the Pb²⁺-specific DNA2, the designed biosensor also showed low false-positive signal rates with other metal ions in real-world examples. Therefore, this strategy has the potential for practical application in environmental monitoring. Graphical abstract ᅟ.

A Pb2+ ionic gate with enhanced stability and improved sensitivity based on a 4′-aminobenzo-18-crown-6 modified funnel-shaped nanochannel

An ionic gate for sensing Pb²⁺ based on an emerging advanced funnel-shaped nanochannel system is reported, with enhanced stability and improved sensitivity.

Electroactive crown ester-Cu2+ complex with in-situ modification at molecular beacon probe serving as a facile electrochemical DNA biosensor for the detection of CaMV 35s

A novel electrochemical DNA biosensor has been facilely constructed by in-situ assembly of electroactive 4'-aminobenzo-18-crown-6-copper(II) complex (AbC-Cu2+) on the free terminal of the hairpin-structured molecule beacon. The 3'-SH modified molecule beacon probe was first immobilized on the gold electrode (AuE) surface through self-assembly chemistry of Au-S bond. Then the crow ester of AbC was covalently coupled with 5'-COOH on the molecule beacon, and served as a platform to attach the Cu2+ by coordination with ether bond (-O-) of the crown cycle. Thus, an electroactive molecule beacon-based biosensing interface was constructed. In comparison with conventional methods for preparation of electroactive molecule beacon, the approach presented in this work is much simpler, reagent- and labor-saving. Selectivity study shows that the in-situ fabricated electroactive molecule beacon remains excellent recognition ability of pristine molecule beacon probe to well differentiate various DNA fragments. The target DNA can be quantatively determined over the range from 0.10pM to 0.50nM. The detection limit of 0.060pM was estimated based on signal-to-noise ratio of 3. When the biosensor was applied for the detection cauliflower mosaic virus 35s (CaMV 35s) in soybean extraction samples, satisfactory results are achieved. This work opens a new strategy for facilely fabricating electrochemical sensing interface, which also shows great potential in aptasensor and immurosensor fabrication.

2,3,4-Trihydroxy benzophenone as a novel reducing agent for one-step synthesis of size-optimized gold nanoparticles and their application in colorimetric sensing of adenine at nanomolar concentration

2,3,4-trihydroxy benzophenone acts as a novel reducing and stabilizing agent for one-step synthesis of size-optimized Au NPs and used as a probe for colorimetric sensing of adenine.

Simultaneous colorimetric detection of four drugs in their pharmaceutical formulations using unmodified gold nanoparticles as a probe

Schematic representation for the aggregation of unmodified Au NPs induced by four drugs (venlafaxine, imipramine, amlodipine, and alfuzosin).

Malonamide dithiocarbamate functionalized gold nanoparticles for colorimetric sensing of Cu2+ and Hg2+ ions

In this study, a colorimetric probe was developed based on malonamide dithiocarbamate functionalized gold nanoparticles (MA–DTC–Au NPs) for the simultaneous colorimetric detection of Cu²⁺ and Hg²⁺ ions.