Castellino M.

Demarchi D.

Giorcelli M.

Sanginario A.

English

SANGINARIO, ALESSANDRO

DEMARCHI, DANILO

GIORCELLI, MAURO

CASTELLINO, MICAELA

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)

03 August 2020POLITECNICO DI TORINORepository ISTITUZIONALECarbon nanotube electrodes for electrochemiluminescence biosensensors / Sanginario A.; Demarchi D.; Giorcelli M.;Castellino M.. - STAMPA. - 1(2010), pp. 195-198. ((Intervento presentato al convegno International semiconductorconference tenutosi a Sinaia (Romania) nel 11-13 Ottobre 2010.OriginalCarbon nanotube electrodes for electrochemiluminescence biosensensorsPublisher:PublishedDOI:Terms of use:openAccessPublisher copyright(Article begins on next page)This article is made available under terms and conditions as specified in the  corresponding bibliographic description inthe repositoryAvailability:This version is available at: 11583/2379384 since:IEEECARBON NANOTUBE ELECTRODES FOR ELECTROCHEMILUMINESCENCE BIOSENSORSA. Sanginario*, D. Demarchi*, M.Giorcelli**, M. Castellino***Electronics Dept. - Politecnico di Torino, Torino, ItalyE-mail: alessandro.sanginario@polito.it – danilo.demarchi@polito.it**Physics Dept. - Politecnico di Torino, Torino, Italy*E-mail: mauro.giorcelli@polito.it – micaela.castellino@polito.itAbstractThe present application is based on the use of carbon  nanotubes  (CNTs)  for  biomolecular  analysis  using  electrochemiluminescence (ECL) detection technique  [1]-[9]. For this purpose we have grown self standing  blocks  of  multi-wall  CNTs  (MWCNTs).  The  blocks  were subsequently  back-contacted and encapsulated  into  epoxy  resin  for  their  use  as  voltammetric  electrodes.  A  ruthenium-complex  solution  has  been  used as ECL label. It has been observed a periodical  light emission that lasts for hundreds of cycles, likely  due  to  the  CNTs  structure.  Thanks  to  a  data-processing algorithm which exploits this  behaviour,  the experiments show that it  is possible to obtain a  great increase in detection limit.Keywords: biosensor, ECL, carbon nanotubes1. INTRODUCTIONSince  their  discovery  [10],  carbon nanotubes (CNTs) have attracted tremendous attention due to their extraordinary electronic, mechanical and chemical properties, which make them a strategic material  for  electroanalytical  applications.  In presented work CNTs have been considered for use  in  biodevices,  aimed  at  the  detection  of various biomolecules [11], in order to overcome the  detection  limits  coming  from  classical electrodes  used  in  electrochemiluminescence (ECL) and cyclic voltammetry (CV) tests. ECL is  a  powerful  electrochemical  technique  for measuring  various  biomolecules  in  very  low quantity.  Its  principle  is  quite  similar  to photoluminescence  (PL):  to  stimulate  a luminescent  chemical  label  and  to  readout  its response  in  terms  of  emitted  light.  Differently from PL in which the stimuli is optic (usually a laser), in ECL the source of excitation is electric (electrodes).  It  is  easy  to  understand that  ECL has a big improvement in the SNR because the light  collected  comes  only  from  the electrochemical  label  and  not  also  from  the excitation  source.  Moreover,  required instrumentation  is  much  less  expensive  and scalable  to  the  micro  and  nano  scale.  For  this purpose  we  have  created  an  electrode  using  a millimeter  long  column  of  vertically  aligned multi  walls  CNTs  growth  by  chemical  vapour deposition  (CVD)  process  on  patterned  silicon substrates.  The  column was  subsequently  back-contacted and encapsulated with epoxy resin as electrical insulator and sealant. This electrode has been  used  in  combination  with  other  two electrodes,  one  made  of  gold  (as  counter electrode)  and one made of silver  (as reference electrode), in order to create an electrochemical cell as shown in fig. 1.2.1. FABRICATION AND TECHNOLOGYThermal-CVD  process  for  growing  multi-wall carbon nanotubes (MWCNTs) was performed at 850° C in a horizontal  quartz tube housed in a cylindrical  furnace.  An  inert  gas  flow  (N2) carried  the  gas  mixture  of  carbon  precursor (commercial  camphor)  and  metal  catalyst (ferrocene 98% purity  in  weight,  Aldrich)  after their evaporation. The mix, in a 20/1 mass ratio (precursor/catalyst) has been carried towards the centre of the furnace, where the gases pyrolysis led  to  the  deposition  of  a  CNTs  layer  on  the silicon  patterned  substrate.  For  growth parameters  and  details  see  [12]  and  [13].  The Fig. 1.Schematic view of the whole system: a personal  computer controls the potentiostat for the sweep  generation and a PMT collects the light generated by  the electrochemical reaction.geometry of the cylindrical electrodes has been drawn  on  silicon  surface  using  the photolithography technique. Positive photoresist (HPR 504, Fujifilm) thin layer (1.4µm thick) has been masked, exposed to UV light and removed with its proper solution, leaving resist pillars on the  silicon  surface.  The  substrate  has  been subsequently covered with a double metal layer (5 nm of titanium as adhesion layer, and 100 nm of  copper)  using  the  thermal  evaporation technique in high vacuum (  10∼ −7 torr).  Resist has  been  subsequently  removed with  a  lift-off procedure in  acetone,  leaving round metal-free areas of the desired geometry on the substrate, prior to CNTs deposition (fig. 2).2.2. MACRO-ELECTRODE CONSTRUCTIONFor  building  a  manageable  and  mechanically stable electrode, with the correct wire contact, a copper wire or a tin connector has been pasted, with conductive glue, on one side of the resulting cylinder. Then the new electrode has been covered with epoxy  resin  leaving  the  other  side  free.  The epoxy  resin  cover  serves  both  as  electrical insulator and as mechanical protection, as can be seen in the final result reported in fig. 3. A  complete  electrochemical  cell  was  realized associating the CNT electrode (used as working electrode)  to  a  gold electrode (used as  counter electrode) and to a silver one (used as reference electrode)2.3. CHEMICALS AND COMPOSITIONSEmitting solution used is based on a compound of  Ruthenium,  Ru(bpy)2+3,  Ruthenium  Tris Bypiridil [1]. The  ruthenium  was   courtesy  prepared  by researchers of University of BolognaStock solution concentration was 10−4 M, buffered with a phosphate solution (PBS) 10−1 M. In other words,  a  concentration  of  about  80  ng/µl  of ruthenium,  in  which  will  be  later  dissolved tripropylamine (TPA) at its solubility limit. From this  stock  solution  were  performed  many measurements at different dilutions in buffer,  in order  to  compare sensitivity  of  the  new system with a classical one. At this stage of the research it was detected ruthenium in solution, also if the final goal of the work will be to detect molecules attached to CNT surface,  as  have been done in several  applications  for  DNA detection systems ([14], [15]). This approach was chosen because it was decided to initially test the feasibility of the device and to find the characteristics, parameters and performances of ECL detection system, then, in  a  second  stage,  experiments  with  DNA attached to CNT surface will be carried on.2.4.  ELECTROCHEMICAL CELL AND COMPLETE SYSTEMIn order to manage the whole system, a custom software and a potentiostat have been built. The software, written in Python language, can manage different  experiments and waveforms,  while the potentiostat has been designed to generate stable cell driving potentials and to collect the very little currents from the voltammetric signal (fig. 1). At the  emitting  voltage  of  the  ruthenium  solution used,  the  chemical  solution  starts  to  emit  light. For  this  reason  the  solution  to  be  analysed  is spotted on a transparent surface on the top of an Fig. 2: Cylindrical CNTs bunch laid down on a silicon surface.Fig. 3: CNTs working electrode covered by  epoxy resin for mechanical stability and electrical insulation.underneath  photomultiplier  (PMT)  in  order  to have  the  maximum collection  of  emitted  light. The PMT (an Hamamatsu H9306-03 was used for  this  purpose)  voltage  is  proportional  to emitted  light  that  is  itself  proportional  to concentration of the solution to be analysed. In order to avoid artefacts and to increase the light detection level the whole system was placed into a  dark  box:  a  completely  dark  environment allows to reach best sensitivity.3. RESULTSIn  order  to  have  a  direct  comparison,  the  first measurement of the solution was done using a classical  electrochemical  cell  with  a  gold working electrode. Then, the same solution was measured  using  the  produced  CNTs  electrodes and  the  comparisons  between  the  two  setups were done. In fig. 4 is reported a graph were is plotted the light intensity trend over increasing dilution for a standard  electrochemical  cell.  It  is  possible  to notice  that  with  gold  working  electrodes  the detection limit is about a 1:50 dilution, in fact a 1:100  dilution  signal  emission  is  no  more detectable. The results obtained by using CNTs electrode were significantly better after a proper data treatment. The improvement is mainly due not only to the highly  increased  contact  area  exhibited  by  the MWCNTs  (40-80  m2/g)  in  comparison  to standard metal  electrodes,  but  in  particular  to  a custom  algorithm  which  exploits  a  very interesting effect  of CNTs electrode,  discovered and recently patented [16] by some of the authors. Fig. 5 shows that the light emission with this type of  electrodes  is  smaller  compared  to  gold electrode  but  it  is  constant  for  a  very  large number of cycles (more than 100). We exploited this  “property”  by  applying  the  concept  of  a common  algorithm  used  in  electronics:  the averaging.  By  averaging  over  many  cycles  of light emission we are able to pull down the noise and consequently to extract weak light emission signals buried into the background noise. Fig. 6 shows  a  portion  of  raw  data  before  they  are processed by our algorithm. As, in this case, the concentration of Ru compound is  very low, the wanted  signal  is  buried  into  the  noise  because only  few photons  reached the  PMT.  Thanks  to our data treatment it has been possible to extract the low signal from that noise thus consequently to  detect  very  low amount  of  chemical  analyte (fig. 7). As said before, in our case, the detection limit of the standard electrochemical cell with a gold  working  electrode  was  a  dilution  of  1:50 (fig. 4). Using CNT working electrode, associated to our customized algorithm, Fig. 4: Graph showing ECL signal against ruthenium dilutions using a standard gold working electrode.Fig. 5: Extract of some constant emission cycles of  the CNTs working electrodeFig. 6: Portion of raw data (i.e. without data  treatment) in which the useful signal is buried into the  noiseFig. 7: Same portion of data shown in fig. 6 after our  algorithm for adiluition of 1:1000. The signal has  been extracted from the noiseit  was possible  improve the SNR and to reach dilutions up to 1:1000 and even more, as can be seen in fig. 7, where for a dilution of 1:1000 the signal is perfectly extracted from the noise and clearly detectable. This dilution, considering the concentration  of  the  stock  solution  used, corresponds to a ruthenium concentration of 80 pg/µl (i.e. a 10−7 M molar detection level).4. CONCLUSIONS Obtained results show that CNTs can be used in ECL and voltammetry devices as electrodes, and that their use lead to an improvement in detection limit.  Such  electrodes  present  an  unexpected behavior of constant signal emission  likely due to their large surface area and their disordered-matrix shape. This effect has been exploited to obtain  a  great  improvement  of  the  minimum signal  noticeable,  having  a  gain  of  at  least  20 times.  This  improvement  is  essential  for detection  of  biomolecules  such  as  DNA  or proteins and it will give the possibility to realize more efficient and precise biomedical diagnostic devices. ACKNOWLEDGEMENTThe authors would like to thank Dr. Leopoldo Della  Ciana  of  Cyanagen  Srl,  Dr.  Simone Zanarini,  Prof.  Francesco  Paolucci  of “Ciamician”,  University  of  Bologna,  for  their help on chemical topics and Dr. Stefano Bianco for  helping  in  the  preparation  of  CNTs electrodes.REFERENCES[1] R. D. Gerardi, N. W. Barnett, S. W. Lewis, “Analytical applications of tris(2,20-bipyridyl) ruthenium(III) as a chemiluminescent reagent”,Analytica Chimica Acta, vol. 378 (1999), pp. 1-41[2] X. Yin, S. Dong, E. Wang, “Analytical applications of the electrochemiluminescence of tris (2,2-bipyridyl) ruthenium and its derivatives”, Trends in Analytical Chemistry, 2004, 23(6), pp. 432-441[3] M. M. Richter, “Electrochemiluminescence (ECL)”, Chem. Rev., vol 104 (2004), pp. 3003-3036[4] A. W. Knight, “A review of recent trends in analytical applications of electrogenerated chemiluminescence”, Trends in analytical chemistry,1999, 18(1), pp. 47-62 [5] K. A. Fahnrich, M. Pravda, G. G. Guilbault, “Recent applications of electrogenerated chemiluminescence in chemical analysis”, Talanta, 2001, 54, pp. 531-559[6] A. J. Bard, “Electrogenerated chemiluminescence”, Marcel Dekker, New York, 2004[7] B. A. Gorman, P. S. Francis, N. W. Barnett, “Tris(2,29-bipyridyl) ruthenium(II) chemiluminescence”, Analyst, 2006, 131, pp. 616639[8] W. Miao, “Electrogenerated Chemiluminescence and Its Biorelated Applications”, Chem. Rev., 2008, 108, pp. 25062553[9] H. Wei, E. Wang, “Solid-state electrochemiluminescence of tris(2,2- bipyridyl) ruthenium”, Trends in Analytical Chemistry, 2008, 27(5), pp. 447-459[10] S. Iijima, “Helical microtubules of graphitic carbon”, Nature 314 (1991), pp. 5658 [11] Z. Xu, X. Chen, X. Qu, J. Jia, S. Dong, “Single wall carbon nanotube based voltammetric sensor and biosensor”, Biosensors and Bioelectronics, vol. 20 (2004), pp. 579584[12] S. Musso, S. Porro, M. Rovere, A. Chiodoni, A. Tagliaferro, “Physical and mechanical properties of thick self standing layers of multiwall carbon nanotubes”, Diamond and Related Materials, vol. 16 (2007), pp. 1174-1178[13] S. Musso, S. Porro, M. Giorcelli, A. Chiodoni, C. Ricciardi, A. Tagliaferro, “Macroscopic growth of carbon nanotube mats and their mechanical properties”, Carbon / Letters to the Editor, vol. 45 (2007), pp .1133-1136[14] H. Cai, X. Cao, Y. Jiang, P. He, Y. Fang, “Carbon nano tube-enhanced electrochemical DNA biosensor for DNA hybridization detection”, Anal. Bioanal. Chem. (2003), pp. 375:287- 293[15] J. Li, H. T. Ng, A. Cassell, W. Fan, H. Chen, Q. Ye, J. Koehne, J. Han, M. Meyyappan, Carbon Nanotube Nanoelectrode Array for Ultrasensitive DNA Detection, NANO LETTERS, 2003, Vol.3 N 5, 597-602[16] D. Demarchi, P. Civera, A. Sanginario, R. Canova, T. Marco, L. Della Ciana, Procedimento per la generazione e l’analisi di segnali di elettrochemiluminescenza e relativo sistema, Patent Number: TO201000212, 19/03/2010.

Carbon nanotube electrodes for electrochemiluminescence biosensensors

https://iris.polito.it/retrieve/handle/11583/2379384/53759/Carbon%20nanotubes%20electrodes%20for%20electrochemiluminescence%20biosensor.pdf

Carbon nanotube electrodes for electrochemiluminescence biosensensors

Abstract

Similar works

Full text

Available Versions

PORTO@iris (Publications Open Repository TOrino - Politecnico di Torino)