Colorimetric-SERS dual-mode sensing of Pb(II) ions in traditional Chinese medicine samples based on carbon dots-capped gold nanoparticles as nanozyme

Peroxidase (POD)-mimicking nanozymes have got great progress in the sensing field, but most nanozyme assaying systems are built with a single-signal output mode, which is vulnerable to the effect of different factors. Thus, establishment of a dual-signal output mode is necessary for acquiring dependable and durable performance. This work described an Fe doped noradrenaline-based carbon dots and Prussian blue (Fe,NA-CDs/PB) nanocomposite as a POD-like nanozyme and modified gold nanoparticles (AuNPs) for the colorimetric and surface-enhanced Raman scattering (SERS) dual-mode sensor of Pb(II) in traditional Chinese medicine samples. With 2,2'-azino-bis-(3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) and 3,3',5,5'-tetramethylbenzidine (TMB) as the substrates, it was found that the addition of Pb(II) inhibited the POD-like activity of Fe,NA-CDs/PB and AuNPs, so it was used for colorimetric and SERS dual-mode assays. The POD-like activity was shown to be a "ping-pong" catalytic mechanism, whereas the addition of Pb(II) produced noncompetitive inhibition with modulatory effects on Fe,NA-CDs/PB. The linear response range for colorimetric and SERS sensor detection of Pb(II) was 0.01-1.00 mg/L with the detection limit of 5 μg/L and 8 μg/L, respectively. This dual-mode detection system shows excellent selectivity. More importantly, the Pb(II) in traditional Chinese medicine samples have successfully assayed with good recovery from 90.4 to 108.9 %.

Rapid and sensitive in situ detection of heavy metals in fish using enhanced Raman spectroscopy

Heavy metals have been widely applied in industry, agriculture, and other fields because of their outstanding physics and chemistry properties. They are non-degradable even at low concentrations, causing irreversible harm to the human and other organisms. Therefore, it is of great significance to develop high accuracy and sensitivity as well as stable techniques for their detection. Raman scattering spectroscopy and atomic absorption spectrophotometer (AAS) were used parallelly to detect heavy metal ions such as Hg, Cd, and Pb of different concentrations in fish samples. The concentration of the heavy metals is varied from 5 ppb to 5 ppm. Despite the satisfactory recoveries of AAS, their drawbacks are imperative for an alternative technique. In Raman scattering spectroscopy, the intensities and areas of the characteristic peaks are increased with increasing the concentration of the heavy metals. For Hg concentration ≥ 1 ppm, a slight shift is observed in the peak position. The obtained values of peak intensity and peak area are modeled according to Elvoich, Pseudo-first order, Pseudo-second order, and asymptotic1 exponential model. The best modeling was obtained using the Elovich model followed by the asymptotic1 exponential model. The introduced Raman spectroscopy-based approach for on-site detection of trace heavy metal pollution in fish samples is rapid, low-cost, and simple to implement, increasing its visibility in food safety and industrial applications.

A Comprehensive Review on Water Quality Monitoring Devices: Materials Advances, Current Status, and Future Perspective

Water quality monitoring has become more critical in recent years to ensure the availability of clean and safe water from natural aquifers and to understand the evolution of water contaminants across time and space. The conventional water monitoring techniques comprise of sample collection, preservation, preparation, tailed by laboratory testing and analysis with cumbersome wet chemical routes and expensive instrumentation. Despite the high accuracy of these methods, the high testing costs, laborious procedures, and maintenance associated with them don't make them lucrative for end end-users and field testing. As the participation of ultimate stakeholders, that is, common man for water quality and quantity can play a pivotal role in ensuring the sustainability of our aquifers, thus it is essential to develop and deploy portable and user-friendly technical systems for monitoring water sources in real-time or on-site. The present review emphasizes here on possible approaches including optical (absorbance, fluorescence, colorimetric, X-ray fluorescence, chemiluminescence), electrochemical (ASV, CSV, CV, EIS, and chronoamperometry), electrical, biological, and surface-sensing (SPR and SERS), as candidates for developing such platforms. The existing developments, their success, and bottlenecks are discussed in terms of various attributes of water to escalate the essentiality of water quality devices development meeting ASSURED criterion for societal usage. These platforms are also analyzed in terms of their market potential, advancements required from material science aspects, and possible integration with IoT solutions in alignment with Industry 4.0 for environmental application.

A review on recent advances in the applications of surface-enhanced Raman scattering in analytical chemistry

This review is focused on recent developments of surface-enhanced Raman scattering (SERS) applications in Analytical Chemistry. The work covers advances in the fabrication methods of SERS substrates, including nanoparticles immobilization techniques and advanced nanopatterning with metallic features. Recent insights in quantitative and sampling methods for SERS implementation and the development of new SERS-based approaches for both qualitative and quantitative analysis are discussed. The advent of methods for pre-concentration and new approaches for single-molecule SERS quantification, such as the digital SERS procedure, has provided additional improvements in the analytical figures-of-merit for analysis and assays based on SERS. The use of metal nanostructures as SERS detection elements integrated in devices, such as microfluidic systems and optical fibers, provided new tools for SERS applications that expand beyond the laboratory environment, bringing new opportunities for real-time field tests and process monitoring based on SERS. Finally, selected examples of SERS applications in analytical and bioanalytical chemistry are discussed. The breadth of this work reflects the vast diversity of subjects and approaches that are inherent to the SERS field. The state of the field indicates the potential for a variety of new SERS-based methods and technologies that can be routinely applied in analytical laboratories.

Liquid Cladding Mediated Optical Fiber Sensors for Copper Ion Detection

We present a label-free optical fiber based sensor device to detect copper ions (Cu2+) in water. A multimode optical fiber, with its polymer cladding removed along a 1-cm length, is used for the optical sensor head, where the injected Cu2+ in the liquid phase acts as a liquid cladding for the optical mode. The various Cu2+ concentrations modulate the numerical aperture (NA) of the liquid cladding waveguide part. The degree of NA mismatch between the liquid cladding and solid cladding guided parts gives rise to an optical power transmittance change, forming the sensing principle. The presented liquid cladding fiber sensor exhibits a minimum resolvable refractive index of 2.48 × 10-6. For Cu2+ detection, we functionalize the sensor head surface (fiber core) using chitosan conjugated ethylenediaminetetraacetic acid (EDTA) which captures Cu2+ effectively due to the enhanced chelating effects. We obtain a limit of detection of Cu2+ of 1.62 nM (104 ppt), which is significantly lower than the tolerable level in drinking water (~30 µM), and achieve a dynamic range of 1 mM. The simple structure of the sensor head and the sensing system ensures the potential capability of being miniaturized. This may allow for in-situ, highly-sensitive, heavy metal sensors in a compact format.

Review of SERS Substrates for Chemical Sensing

The SERS effect was initially discovered in the 1970s. Early research focused on understanding the phenomenon and increasing enhancement to achieve single molecule detection. From the mid-1980s to early 1990s, research started to move away from obtaining a fundamental understanding of the phenomenon to the exploration of analytical applications. At the same time, significant developments occurred in the field of photonics that led to the advent of inexpensive, robust, compact, field-deployable Raman systems. The 1990s also saw rapid development in nanoscience. This convergence of technologies (photonics and nanoscience) has led to accelerated development of SERS substrates to detect a wide range of chemical and biological analytes. It would be a monumental task to discuss all the different kinds of SERS substrates that have been explored. Likewise, it would be impossible to discuss the use of SERS for both chemical and biological detection. Instead, a review of the most common metallic (Ag, Cu, and Au) SERS substrates for chemical detection only is discussed, as well as SERS substrates that are commercially available. Other issues with SERS for chemical detection have been selectivity, reversibility, and reusability of the substrates. How these issues have been addressed is also discussed in this review.