A frugal implementation of Surface Enhanced Raman Scattering for sensing Zn2+ in freshwaters – In depth investigation of the analytical performances

Abstract

Surface enhanced Raman Scattering (SeRS) has been widely praised for its extreme sensitivity but has not so far been put to use in routine analytical applications, with the accessible scale of measurements a limiting factor. We report here on a frugal implementation of SeRS dedicated to the quantitative detection of Zn 2+ in water, Zn being an element that can serve as an indicator of contamination by heavy metals in aquatic bodies. the method consists in randomly aggregating simple silver colloids in the analyte solution in the presence of a complexometric indicator of Zn 2+ , recording the SeRS spectrum with a portable Raman spectrometer and analysing the data using multivariate calibration models. the frugality of the sensing procedure enables us to acquire a dataset much larger than conventionally done in the field of SERS, which in turn allows for an in-depth statistical analysis of the analytical performances that matter to end-users. in pure water, the proposed sensor is sensitive and accurate in the 160-2230 nM range, with a trueness of 96% and a precision of 4%. Although its limit of detection is one order of magnitude higher than those of golden standard techniques for quantifying metals, its sensitivity range matches Zn levels that are relevant to the health of aquatic bodies. Moreover, its frugality positions it as an interesting alternative to monitor water quality. critically, the combination of the simple procedure for sample preparation, abundant SERS material and affordable portable instrument paves the way for a realistic deployment to the water site, with each Zn reading three to five times cheaper than through conventional techniques. It could therefore complement current monitoring methods in a bid to solve the pressing needs for large scale water quality data. The management of water resources necessitates large volumes of water quality data so as to identify sources of pollution, assess contaminant levels in aquatic ecosystems, control the safety of drinking water, safeguard the reuse of wastewater or ascertain the efficiency of remediation actions 1. This need was recognised by the European Union and the United States as early as in the mid-nineties, in reports where representatives of both governments recommended moving away from laboratory-based analytical procedures, which could not sustain suitable throughputs of water quality data 2,3. They called instead for the development of analytical methods and sensors operated directly on site, at a high temporal frequency and possibly in a continuous fashion. Yet in the current decade, major international (development) organisations are still calling for improved analytical tools capable of high throughput water quality monitoring 4-6 .

Applications of surface‐enhanced Raman spectroscopy based on portable Raman spectrometers: A review of recent developments

“…The method exhibited high sensitivity with a LOD of 0.72 ppb. [64] In addition, SERS methods, for the analysis of other heavy metals in the environment using a portable Raman spectrometer, have also been developed, such as zinc ion (Zn 2+ ), [65] arsenic(III), [66] lead(II) [67] etc. used increasingly to prevent and treat various diseases in fish with the rapid development of aquaculture.…”

A new look at an old classic: implementation of a SERS-based water hardness titration

“…through building a signal calibration model. 14 The significant difference is, however, that it took much less time to achieve them using the complexometric probe in indicator mode: where it took 80 samples to build the calibration model and 6 replicate measurements to achieve 5% precision in spectrophotometric mode, one water hardness titration required only 18 samples, in a single titration series. Moreover, the calibration model in the previous study was valid over just one decade of metal analyte concentration, whereas the present detection scheme works over a concentration range extended 2.5 folds.…”

“…We recently demonstrated that calibration is actually the largest driver of the consolidated cost of a metal ion analysis by SERS. 14 However, quantification does not need to rely on calibration of a spectral signal.…”