Enhancement of electrode performance through surface modification using carbon nanotubes and porous gold nanostructures

Recently, the demand for the sensitive detection of nanomaterials and biomolecules has been increasing for evaluating the toxicity of nanomaterials and early diagnosis of diseases. Although many studies have developed new detection assays, these are heavily influenced by the capabilities of the detection equipment. Therefore, the aim of the present study was to improve electrode performance by modifying the surface of the detection electrode using a simple method. Electrode surface modification was performed using carbon nanotubes (CNT) and porous gold nanostructures (NS) with excellent electrical and chemical properties. Through the simple physical deposition of CNT and electrochemical reduction of NS, the increasement of the electrode surface area was achieved. Because of the CNTs attached to the electrodes at the first step, the metal ions constituting the NS can adhere well to the electrodes. Nanoparticles with a porous structure can be generated through electrochemical reduction (cyclic voltammetry) of metal ions attached to electrodes. Consequently, the surface area of the electrode increased and electrochemical performance was improved (confirmed by atomic force microscopy, Nyquist plot and Bode plot). To quantitatively confirm the improvement of electrode performance according to the surface change through the proposed treatment technique, DNA was detected. Unlike previous surface modification studies, the developed surface treatment technique can be applied to a variety of detection equipment. To confirm this, the detection was performed using two detection devices with different operating principles. DNA detection using the two types of equipment confirmed that the detection limit was increased by approximately 1000-fold through applying a simple surface treatment. In addition, this method is applicable to detect various sizes of nanomaterials. The method proposed in this study is simple and has the advantage that it can be applied to various devices and various materials.

Portable solid sensor supported in nylon for silver ion determination: testing its liberation as biocide

This paper reports the fabrication and utility of a new solid sensor, which allows the quantitation of silver ions acting as catalyst at the low micromolar level. The optical sensor was prepared by incorporating both reagents, pyrogallol red (PGR) and 1,10-phenanthroline (Phen), in a nylon membrane. The effect of parameters in determining silver-catalyzed oxidation of PGR by persulfate in the presence of Phen as an activator was studied and optimized for achieving suitable sensitivity. Semiquantitative analysis can be performed by visual inspection of the color of the sensor by comparing it with standard responses and quantitative analysis can be carried out by its diffuse reflectance (DR) measurement or by a digital image-processing tool (GIMP) using a smartphone. The sensor exhibited a linear relationship toward Ag(I) concentrations ranging from 0.4 to 10 μM or 1-25 μM and limits of detection of 0.1 μM or 0.3 μM for incubation times of 50 and 30 min, respectively. The relative standard deviation achieved for several batches of sensors was around 2%. The analysis of water samples from tap and refrigerating circuits containing solid biocides, which leach silver ions, prove that this portable and sustainable sensor is successfully operational in real situations. Graphical abstract.

Metal Cation Detection in Drinking Water

Maintaining a clean water supply is of utmost importance for human civilization. Human activities are putting an increasing strain on Earth’s freshwater reserves and on the quality of available water on Earth. To ensure cleanliness and potability of water, sensors are required to monitor various water quality parameters in surface, ground, drinking, process, and waste water. One set of parameters with high importance is the presence of cations. Some cations can play a beneficial role in human biology, and others have detrimental effects. In this review, various lab-based and field-based methods of cation detection are discussed, and the uses of these methods for the monitoring of water are investigated for their selectivity and sensitivity. The cations chosen were barium, cadmium, chromium, copper, hardness (calcium, magnesium), lead, mercury, nickel, silver, uranium, and zinc. The methods investigated range from optical (absorbance/fluorescence) to electrical (potentiometry, voltammetry, chemiresistivity), mechanical (quartz crystal microbalance), and spectrometric (mass spectrometry). Emphasis is placed on recent developments in mobile sensing technologies, including for integration into microfluidics.

A Sensitive Fluorescence Biosensor for Silver Ions (Ag+) Detection Based on C-Ag+-C Structure and Exonuclease III-Assisted Dual-Recycling Amplification

A C-Ag⁺-C structure-based fluorescence biosensor with novel combination design of exonuclease III (Exo III) dual-recycling amplification is proposed for the application of silver ions (Ag⁺) detection. Since oligo-1 involves C-C mismatches, the presence of Ag⁺ can be captured to form C-Ag⁺-C base pairs, which results in a double-helix structure with a blunt terminus. The double-helix structure can be cleaved by EXO III to release short mononucleotide fragments (trigger DNA) and Ag⁺. Released Ag⁺ can form new bindings with oligo-1, and other trigger DNA can be produced in the digestion cycles. Hybridization with the signal DNA (oligo-2) transforms a trigger DNA into double-stranded DNA with blunt terminus which can be cleaved by Exo III to reproduce the trigger DNA and form guanine- (G-) quadruplex DNA. The trigger DNA returns free to the solution and hybridizes with another signal DNA, which realizes the dual-recycling amplification. The G-quadruplex DNA can be reported by N-methylmesoporphyrin IX (NMM), a specific G-quadruplex DNA fluorochrome. This method allows Ag⁺ to be determined in the 5 to 1500 pmol/L concentration range, with a 2 pmol/L detection limit, and it has been successfully applied to the detection of Ag⁺ in real samples.

Facile preparation of orange-emissive carbon dots for the highly selective detection of silver ions

We have prepared orange-emissive carbon dots, which serve as a highly selective fluorescent method for the detection of silver ions.

Highly sensitive detection of silver ions using a silver-specific DNA based nano-porous micro-resonator

Detection of silver ions is based on a frequency shift of a resonator upon interaction between silver ions and cytosine bases.