sensors Review Recent Advances on Detection of Insecticides Using Optical Sensors Nurul Illya Muhamad Fauzi 1, Yap Wing Fen 1,2,*, Nur Alia Sheh Omar 1,2 and Hazwani Suhaila Hashim 2 1 Functional Devices Laboratory, Institute of Advanced Technology, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; [email protected] (N.I.M.F.); [email protected] (N.A.S.O.) 2 Department of Physics, Faculty of Science, Universiti Putra Malaysia, Serdang 43400, Selangor, Malaysia; [email protected] * Correspondence: [email protected] Abstract: Insecticides are enormously important to industry requirements and market demands in agriculture. Despite their usefulness, these insecticides can pose a dangerous risk to the safety of food, environment and all living things through various mechanisms of action. Concern about the environmental impact of repeated use of insecticides has prompted many researchers to develop rapid, economical, uncomplicated and user-friendly analytical method for the detection of insecticides. In this regards, optical sensors are considered as favorable methods for insecticides analysis because of their special features including rapid detection time, low cost, easy to use and high selectivity and sensitivity. In this review, current progresses of incorporation between recognition elements and optical sensors for insecticide detection are discussed and evaluated well, by categorizing it based on insecticide chemical classes, including the range of detection and limit of detection. Additionally, this review aims to provide powerful insights to researchers for the future development of optical sensors in the detection of insecticides. Citation: Fauzi, N.I.M.; Fen, Y.W.; Omar, N.A.S.; Hashim, H.S. Recent Keywords: insecticides; optical sensor; recognition element Advances on Detection of Insecticides Using Optical Sensors. Sensors 2021, 21, 3856. https://doi.org/10.3390/ s21113856 1. Introduction Pesticides are chemical categories that have been designed to protect crops by pre- Academic Editor: venting, destroying, repelling or mitigating any pests [1]. There are many different types of Radhakrishna Prabhu pesticides in industries such as insecticides, rodenticides, herbicides, fungicides, biocides and similar chemicals [2]. They are categorized according to their chemical forms and Received: 14 February 2021 the types of pests that they kill [3]. The first major synthetic class of pesticides that has Accepted: 24 April 2021 Published: 3 June 2021 been widely used is insecticide [4]. According to United States Environmental Protection Agency, insecticide is commonly used in the agricultural, industrial applications, pub- Publisher’s Note: MDPI stays neutral lic health, commercial applications and households. A variety of different insecticides with regard to jurisdictional claims in such as organophosphates, carbamates, neonicotinoids, pyrethroids or pyrethrins and published maps and institutional affil- organochlorines are classified according to their chemical classes [5]. iations. Today, organophosphates account for around 50% of the chemical pesticides used in controlling the pests. The chemical organophosphates work by disrupting an enzyme in the body called acetylcholinesterases that control the nerve signals in the pest’s body [6]. Carbamates insecticides also play a similar mode as organophosphates. Although they have a similar mechanism of action to that of acetylcholinesterase (AChE) inhibition (phos- Copyright: © 2021 by the authors. Licensee MDPI, Basel, Switzerland. phorylation by organophosphates and carbamylation by carbamates), organophosphates This article is an open access article can bind to AChE irreversibly, meanwhile carbamates bind to AChE reversibly [7]. In distributed under the terms and addition, the toxicity of carbamates is similar to that of organophosphate pesticides with a conditions of the Creative Commons duration typically less than 24 h [8]. In addition, neonicotinoids are a fairly new type of Attribution (CC BY) license (https:// insecticide that have been used over the last 20 years to control a variety of pests, especially creativecommons.org/licenses/by/ sap-feeding insects such as cereal aphids and root-feeding grubs. Like nicotine, neoni- 4.0/). cotinoids work effectively by binding to nerve cell receptors that normally respond to the Sensors 2021, 21, 3856. https://doi.org/10.3390/s21113856 https://www.mdpi.com/journal/sensors Sensors 2021, 21, x FOR PEER REVIEW 2 of 42 neonicotinoids work effectively by binding to nerve cell receptors that normally respond Sensors 2021, 21, 3856 to the neurotransmitter acetylcholine. When neonicotinoids over-excite neurons2 of 39 at high doses, it might lead to epileptic symptoms, cell death or inactivation of the nerve cells [9]. In comparison, neonicotinoids are less toxic to birds and mammals compared to organo- neurotransmitterphosphates and acetylcholine. carbamates [10]. When Subsequently, neonicotinoids the over-excite uses of neuronspyrethrins at high have doses, increased it rap- mightidly with lead tothe epileptic declining symptoms, use of cell organophosph death or inactivationates, carbamates of the nerve and cells [neonicotinoids.9]. In compar- Pyre- ison,thrin neonicotinoids is a botanical are insecticide less toxic derived to birds andfrom mammals chrysanthemum compared flowers. to organophosphates It became a popular andinsecticide carbamates for [10the]. Subsequently,control of agricultural the uses of pests. pyrethrins Apart have from increased that, pyrethrin rapidly with can the also fight decliningmosquito-borne use of organophosphates, diseases. It works carbamates by altering and neonicotinoids. nerve function, Pyrethrin in the is atarget botanical insect pests insecticide derived from chrysanthemum flowers. It became a popular insecticide for the which can causes paralysis in, and finally resulting in death. The small quantity used of control of agricultural pests. Apart from that, pyrethrin can also fight mosquito-borne diseases.pyrethrins It works for the by alteringpests controls nerve function, making in them the target competitively insect pests cost-effective which can causes [11]. To in- paralysiscrease the in, pyrethrin’s and finally resulting stability in on death. sunlight The smallexposure, quantity the used chemical of pyrethrins structure for of the pyrethrin pestshas been controls modified making and them it competitively is called pyrethroid cost-effective [12]. [11 Lastly,]. To increase organochlorines the pyrethrin’s insecticides stabilityhave also on been sunlight used exposure, extensively the chemical in agricultur structuree and of pyrethrin mosquito has control. been modified The major and itdifference isbetween called pyrethroid pyrethrin [12 and]. Lastly, organochlorine organochlorines is the insecticides way it works have to also kill beeninsects. used Organochlorine exten- sivelycompounds in agriculture work on and insects mosquito by opening control. Thethe majorsodium difference ion channel between in insect pyrethrin neurons and or nerve organochlorinecells, spontaneously is the way causing it works them to killto spasm, insects. fire Organochlorine and eventually compounds die [13,14]. work on insects by opening the sodium ion channel in insect neurons or nerve cells, spontaneously Despite insecticide usefulness in many industries, excessive use of it can give a per- causing them to spasm, fire and eventually die [13,14]. niciousDespite impact insecticide on the environment usefulness in and many ecosystem. industries, It excessive can cause use air of pollution, it can give water a pollu- pernicioustion, soil impactpollution, on thefood environment and water and contamination ecosystem. It that can causewill pose air pollution, a great waterdanger to the pollution,human body soil pollution, [15]. This food happen and watered because contamination insecticides that willwere pose secreted a great into danger the to soils and thegroundwater human body that [15]. may This end happened up in becausedrinking insecticides water. Additionally, were secreted the into spray the soils of andinsecticides groundwatercan drift and that pollute may endthe upair inthat drinking can enter water. the Additionally, body by inhaling the spray aerosols, of insecticides dust and vapor, canwhereas drift and oral pollute exposure the air to that the can insecticides enter the body can bybe inhalinghappened aerosols, during dust the and consume vapor, of food whereasand water oral or exposure direct contact to the insecticideswith the skin can [16] be. happened Over time, during the chemical the consume will ofbio-accumulate food and water or direct contact with the skin [16]. Over time, the chemical will bio-accumulate in the body. The effects of insecticides on human health depend on the toxicity of the in the body. The effects of insecticides on human health depend on the toxicity of the chemicalschemicals and and the the exposure exposure period period [17]. [17]. The simplestThe simplest examples examples that have that high have risk high with risk with thisthis toxicity toxicity are are farm farm workers workers and their and families.their fami Theylies. will They experience will experience the greatest the exposure greatest expo- tosure agricultural to agricultural insecticides insecticides through through direct contact direct [18 contact]. The effects [18]. The from effects the exposure from the can exposure becan mild be skinmild irritation, skin irritation, tumor, genetic