Sensors and Actuators B 158 (2011) 423–426 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical journa l h o mepage: www.elsevier.com/locate/snb Short communication Asparagine quantification in cellular culture media using copper modified carbon nanotubes composite electrodes Maria Lorena López Rodriguez a,b , Guillermina L. Luque a , Carmelo J. Felice b,c , Nancy F. Ferreyra a , Rossana E. Madrid b,c,∗∗ , Gustavo A. Rivas a,∗∗ , Carla E. Giacomelli a,∗ a INFIQC, Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina b Laboratorio de Medios e Interfases (LAMEIN), Departamento de Bioingeniería, Facultad de Ciencias Exactas y Tecnología, Universidad Nacional de Tucumán, 4000 Tucumán, Argentina c Instituto Superior de Investigaciones Biológicas, INSIBIO, CONICET, 4000 Tucumán, Argentina a r t i c l e i n f o Article history: Received 19 March 2011 Received in revised form 13 May 2011 Accepted 22 May 2011 Available online 27 May 2011 Keywords: Streptomyces Asparagine Cellular culture media Carbon nanotubes Copper Amperometric sensor a b s t r a c t Direct quantification of Asparagine (Asp) in a Streptomyces sp. M7 (SM7) culture medium was performed using multi-wall carbon nanotubes composite electrodes modified with copper microparticles (CNTPE- Cu). A sensitive and fast response is achieved at CNTPE-Cu after additions of SM7 cultures supernatant, without interference of the culture medium components. This response allows determining the Asp concentration as a function of the bacteria growth. The results reveal that the SM7 bacteria consume Asp as a carbon and nitrogen sources in the absence of another carbon source such as glucose. © 2011 Elsevier B.V. All rights reserved. 1. Introduction The design of an appropriate fermentation medium for bacte- ria and fungi is of crucial importance since medium composition significantly influences their optimum growth, activity, products yield [1–3], and morphology [4]. There are several reports about the effect of the nature and type of carbon (C), nitrogen (N) or phosphorus sources and trace elements on cell growth, biotransfor- mation, and antibiotic biosynthesis by Streptomyces. For optimum growth and bioactive metabolite production by Streptomyces sp. 201, mannitol and asparagine (Asp) were the most suitable C and N sources, respectively [5]. Benimeli et al. [6] reported that Streptomyces strain M7 was capable to degrade pesticides as C sources. Therefore, to achieve maximum bacteria activity and prod- ucts yield it is necessary to optimize nutrients and environmental conditions. Numerous analytical methods have been used for the quantifi- cation of amino acids. Asp specific assays include chromatographic ∗ Corresponding author at: INFIQC, Departamento de Fisicoquímica, Facultad de Ciencias Químicas, Universidad Nacional de Córdoba, Ciudad Universitaria, 5000 Córdoba, Argentina. Tel.: +54 351 4334169; fax: +54 351 4334188. ∗∗ Corresponding authors. E-mail addresses: rmadrid@herrera.unt.edu.ar (R.E. Madrid), grivas@fcq.unc.edu.ar (G.A. Rivas), giacomel@fcq.unc.edu.ar (C.E. Giacomelli). methods [7], and fluorometric [8], and UV–visible spectroscopies [9]. Although in most cases these methods are highly sensitive, they are rather expensive, time consuming and require previous deriva- tization of the amino acids with different methods, for instance the widely used ninhydrin assay [10]. In addition, the amino acid derivatives are not usually very stable and the derivatization pro- cesses introduce interfering compounds that are hardly eliminated. Electrochemical methods have been also used for the quan- tification of amino acids. The amperometric detection of amino acids without previous derivatization was reported by several authors [11–13]. Luque et al. [14] proposed the highly sensitive and selective amperometric quantification of electroactive and non electroactive amino acids, at low potential and physiological pH, without derivatization, using a carbon nanotubes paste electrode modified with copper microparticles (CNTPE-Cu). Here, we propose to optimize a direct method based on CNTPE-Cu to quantify Asp to establish the role of this amino acid as a C and/or N source in Streptomyces sp. M7 culture media. 2. Materials and methods 2.1. Reagents Cu (99% purity) microparticles (-325 mesh, 10% max, +325 mesh, 99%) were acquired from Alfa Aesar. Multi-wall CNT com- 0925-4005/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.snb.2011.05.043