Sensors and Actuators B 161 (2012) 151–155 Contents lists available at SciVerse ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb Sensitivity of Chlorella vulgaris to herbicides. Possibility of using it as a biological receptor in biosensors Georgi D. Rashkov a , Anelia G. Dobrikova a , Irina D. Pouneva b , Amarendra N. Misra c,1 , Emilia L. Apostolova a,∗ a Institute of Biophysics and Biomedical Engineering, Bulgarian Academy of Science, Acad. G. Bonchev Str., Bl. 21, 1113 Sofia, Bulgaria b Institute of Plant Physiology and Genetics, Bulgarian Academy of Science, Acad. G. Bonchev Str., Bl. 21, 1113 Sofia, Bulgaria c Post-Graduate Department of Biosciences & Biotechnology, Fakir Mohan University, Nuapadhi Campus, Balasore-756020, India a r t i c l e i n f o Article history: Received 13 July 2011 Received in revised form 28 September 2011 Accepted 30 September 2011 Available online 18 October 2011 Keywords: Herbicides Chlorella vulgaris Biological receptors Flash induced oxygen yields a b s t r a c t In the present study the sensitivity of Chlorella vulgaris to herbicides was investigated using polarographic oxygen rate electrode and the Pulse-Amplitude-Modulated (PAM) chlorophyll fluorescence measure- ments. Data reveal: (i) higher sensitivity of parameters of photosynthetic oxygen evolution (flash induced oxygen yields and oxygen burst under continuous illumination) in comparison to the widely used param- eters of the chlorophyll fluorescence; (ii) higher sensitivity of oxygen evolution parameters of Chlorella cells to Q B -binding herbicides in comparison to the pea thylakoid membranes; (iii) similar sensitivity of the PAM parameters to herbicides for both Chlorella cells and thylakoid membranes from higher plants. The relationship between the herbicide sensitivity and the kinetic parameters of the oxygen evolution of green algae and higher plants are discussed. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The extensive use of herbicides in agriculture has resulted in raising their levels in soil and water, which is dangerous for the health of all living organisms. Most of the herbicides used in agri- culture, target the quinone binding site Q B , inhibit the photosystem II (PSII) activity and block overall photosynthetic reactions [1,2]. PSII is a light-driven water-plastoquinone oxidoreductase that oxi- dizes water and reduces plastoquinone (PQ) to plastoquinol. It was found that the isolated PSII reaction center complex maintains her- bicide binding activity [3,4]. The binding affinity of the herbicide depends on the amino acid composition of the hydrophobic loop of D1 protein and the binding constant of the herbicide [2,5,6]. The monitoring of pollutants in water and soil is very important to guarantee the health of ecosystems [2]. Therefore the investiga- tions of many researchers are focused on developing the biosensors. The search of high sensitive, rapid and cheap biosensors is an area of intensive research. Some biosensing systems for herbicide detec- tion have used isolated thylakoid membranes, PSII particles or cells ∗ Corresponding author. Tel.: +359 2 979 26 21; fax: +359 2 971 24 93. E-mail address: emya@obzor.bio21.bas.bg (E.L. Apostolova). 1 Present address: Center for Life Sciences, School of Natural Sciences, Central Uni- versity of Jharkhand Ratu-Lohardaga Road, P.O. Brambe-835205, Ranchi, Jharkhand State, India. of algae [6–8]. The limit for the detection of pesticides by biosensors varies according to the bioreceptor used [2]. There are different methods for bioassay of herbicides affecting photosynthetic activities. Some of the methods used routinely are Clark oxygen electrode [9], screen printed carbon-silver electrode [10] and chlorophyll fluorescence [6,11]. Previously we suggested new quick and sensitive method, which can be used for detection of toxic ions or herbicides, for developing biosensors using thylakoid membranes as biological receptors [12–14]. The method is based on the determination of pollutants using parameters of photosyn- thetic oxygen evolution measured by polarographic oxygen rate electrode. Recently we have shown that immobilized pea thylakoid membranes have increased sensitivity and can be used as biolog- ical receptor in biosensors for a prolonged period, applying a new method for herbicide detection, by using polarographic oxygen rate electrode [14]. In the present study the sensitivity of the parameters of PAM chlorophyll fluorescence and photosynthetic oxygen evolution measured by polarographic oxygen rate electrode of Chlorella vul- garis are compared. Chlorella vulgaris isolated from Antarctic soil location was chosen as an object of the present investigation as it is resistant to extreme environmental conditions. The kinetic parameters of the oxygen evolving complex of Chlorella cells, as well as their changes after treatment with Q B -binding herbicides are discussed. 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.09.088