Nanomaterial enabled sensors for environmental contaminants

(2018) 16:95 Willner and Vikesland J Nanobiotechnol https://doi.org/10.1186/s12951-018-0419-1 Journal of Nanobiotechnology Open Access REVIEW Nanomaterial enabled sensors for environmental contaminants Marjorie R. Willner and Peter J. Vikesland* Abstract The need and desire to understand the environment, especially the quality of one’s local water and air, has continued to expand with the emergence of the digital age. The bottleneck in understanding the environment has switched from being able to store all of the data collected to collecting enough data on a broad range of contaminants of environmental concern. Nanomaterial enabled sensors represent a suite of technologies developed over the last 15 years for the highly specific and sensitive detection of environmental contaminants. With the promise of facile, low cost, field-deployable technology, the ability to quantitatively understand nature in a systematic way will soon be a reality. In this review, we first introduce nanosensor design before exploring the application of nanosensors for the detection of three classes of environmental contaminants: pesticides, heavy metals, and pathogens. Keywords: Nanomaterials, Sensor, Detection, Environment, Pesticides, Heavy metals, Pathogens Background Nanomaterial enabled sensors are an exciting technology that provide exquisite detection, on the nanomolar to sub-picomolar level, of environmental contaminants [1–5]. Interest in these sensors stems from their potential for facile, in-field contaminant detection without the need for expensive lab equipment. Many past reviews in this area have grouped sensors based on the signal transduction method [2–5], nanoparticle backbone [7–10], or contaminant class [1, 11, 12], thus leaving one important paradigm virtually untouched: classifying sensors based on the analyte(s) of interest. Because environmental scientists and engineers are often interested in determining if a specific contaminant exists at a field site and if its concentration is above the regulatory limit, there was a need to organize a review based upon the detection of specific contaminants. This review has been developed to address these concerns. First, we summarize the general concepts underlying a nano-enabled sensor and then discuss recent developments in nanomaterial enabled detection of nine specific analytes: two pesticides, four *Correspondence: Department of Civil and Environmental Engineering and the Institute for Critical Technology and Applied Science, Center for Sustainable Nanotechnology (VTSuN), Virginia Tech, Blacksburg, USA metals, and three pathogens. A nearly infinite number of chemicals of environmental concern exist and although it would be impossible to outline all of them, the fundamental nanosensor designs can be seen in the examples outlined within the review. For the reader interested in nanosensors for pharmaceutical detection we direct them to the work of Nagaraj et al. [13] and the reviews of Sanvicens et al. [14] and Cristea et al. on antibiotic detection [15]. Introduction Nanomaterial enabled sensors consist of three components: a nanomaterial(s), a recognition element that provides specificity, and a signal transduction method that provides a means of relaying the presence of the analyte (Fig. 1). These components are not necessarily distinct entities within a sensor, but every nanosensor can be characterized on the basis of these three divisions. Sensors can be designed to detect a single analyte or multiple analytes, termed multiplex detection. In addition to detecting an analyte by producing a signal, a ‘turn-on’ or ‘off/on’ sensor, some of the sensors described below are based on a ‘turn-off ’ or ‘on/off ’ mechanism, where-by a decrease in signal indicates the presence of an analyte. © The Author(s) 2018. This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/ publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Willner and Vikesland J Nanobiotechnol (2018) 16:95 Page 2 of 16 NANOSENSOR DESIGN (i) Environmental Contaminants Pesticides Organochlorines Pyrethroids Pathogens Heavy Metals Legionella pneumophila* Pseudomonas aeruginosa* Naegleria fowleri Escherichia coli Schistosoma spp. Vibrio cholerae and Cholera Toxin* Lead* Mercury* Cadmium* Carbamates* Neonicotinoids* Atrazine* Phenoxy Organophosphates* Chromium * (ii) Number of Analytes Detected 1 >1 Singleplex Multiplex (iii) Nanoprobe Design Nanomaterials Signal Transduction Electrochemical Quantum Dots Magnetic Carbonaceous Noble Metal Optical Magnetic Recognition Elements Proteins Aptamers Antibodies Enzymes (iv) Sensor Deployment Format Solution Microfluidic Device Aqueous Phase Inlets Scaffold/Substrate Oil Inlet Conjugation Pad Sample Pad Control Line Test Line Absorbent Pad Gold Nanoparticle Bacteria Cellulose Hydrogel Fig. 1 Nanosensor design schematic. First, a class and subsequently a specific contaminant of interest is selected (i). The contaminants discussed in this review are denoted with an asterisk. Next, the number of analytes to be detected by the sensor is chosen (ii) and then the probe is designed. A nanoprobe consists of two core elements, a signal transduction method and at least one nanomaterial, and may also include a recognition element (iii). Ultimately, the sensor deployment format is selected (iv) Willner and Vikesland J Nanobiotechnol (2018) 16:95 Nanomaterials Nanomaterials have enabled advances in sensor design such as miniaturization, portability, and rapid signal response times. High surface area to volume ratios and facile surface functionalization make nanomaterials highly sensitive to changes in surface chemistry thus enabling nanosensors to achieve extremely low detection limits. In some cases, the enhanced sensitivity of nanoenabled sensors is due to the fact that nanomaterials are of a similar size as the analyte of interest (e.g., metal ions, pathogens, biomolecules, antibodies, DNA) and are thus capable of interrogating previously unreachable matrices [4]. We briefly introduce three different general nanomaterial classes: quantum dots (QDs), metal nanoparticles, and carbonaceous nanomaterials. Quantum dots QDs are semiconductor nanocrystals with a typical composition MX where M is commonly cadmium (Cd) or zinc (Zn) and X is selenium (Se), sulfur (S), or tellurium (Te). QDs are often coated by a second MX alloy, a shell, to create core/shell QDs with highly tuned properties. Common QDs employed in sensor applications include: CdSe [1 (...truncated)