ARTICLE pubs.acs.org/est Size-Exclusive Nanosensor for Quantitative Analysis of Fullerene C60 Samuel N. Kikandi, Veronica A. Okello, Qiong Wang, and Omowunmi A. Sadik* Center for Advanced Sensors & Environmental System (CASE), Department of Chemistry, State University of New York-Binghamton, P.O. Box 6000 Binghamton, New York 13902-6000, United States Katrina E. Varner US-EPA/NERL Environmental Sciences Division, P.O. Box 93478-3478 Las Vegas, Nevada 89193-3478, United States Sarah A. Burns Department of Chemistry, 359 Natural Sciences Complex, State University of New York-Buffalo, Buffalo, New York 14260-3000, United States bS Supporting Information ABSTRACT: This paper presents the first development of a mass-sensitive nanosensor for the isolation and quantitative analyses of engineered fullerene (C60) nanoparticles, while excluding mixtures of structurally similar fullerenes. Amino- fi β modi ed beta-cyclodextrin ( -CD-NH2) was synthesized and confirmed by 1HNMR as the host molecule to isolate the desired fullerene C60. This was subsequently assembled onto the surfaces of gold-coated quartz crystal microbalance (QCM) electrodes using N-dicyclohexylcarbodiimide/N-hydroxysucci- nimide (DCC/NHS) surface immobilization chemistry to create a selective molecular configuration described as (Au)- fi S-(CH2)2-CONH-beta-CD sensor. The mass change on the sensor con guration on the QCM was monitored for selective ∼ 14À 16 2 quantitative analysis of fullerene C60 from a C60/C70 mixture and soil samples. About 10 10 C60 particles/cm were fi μ successfully quanti ed by QCM measurements. Continuous spike of 200 L of 0.14 mg C60 /mL produced changes in frequency (ÀΔf) that varied exponentially with concentration. FESEM and time-of-flight secondaryÀion mass spectrometry confirmed the validity of sensor surface chemistry before and after exposure to fullerene C60. The utility of this sensor for spiked real-world soil samples has been demonstrated. Comparable sensitivity was obtained using both the soil and purified toluene samples. This work demonstrates that the sensor has potential application in complex environmental matrices. ’ INTRODUCTION or dissolved metal fractions or metal oxidation states. The The discovery of fullerenes in 1985 has ushered in an toxicity, detection and characterization of nanomaterials are explosive growth in the applications of engineered nanomate- dependent on factors such as functionalization, geometry, and À rials (ENMs) and products.1 5 The rapid development of the type of nanomaterials. For example, the cytotoxicity of fullerenes can be decreased following its hydroxylation with 24 nanotechnology and the increasing production of nanomaterials- 3 based products and processes present great opportunities and hydroxyl groups, while the cytotoxicity of carbon nanomater- challenges. To date, the potential impacts of nanomaterials on ials may be enhanced if it was functionalized with carboxylic acid moieties.4 The potential toxicity of fullerenes and its human health and the environment have been limited due 5 to insufficient understanding of the risks associated with its derivatives is still a subject of intense discussion. Some reports development, manipulation and wide-ranging applications. The depict fullerenes as nontoxic while others demonstrate their fi ability to both quench and generate reactive oxygen species- rst step in assessing the risks posed by ENMs is to develop a 6 7 broad array of analytical tools and methods that are applicable (ROS), which may lead to DNA damage. Additionally, to a wide range of manufactured nanomaterials. Conventional methods of assessing the properties and characteristics of raw Received: December 22, 2010 nanomaterials focus on the size distribution and effects. They are, Accepted: May 10, 2011 however, unsuitable for detection and quantification of complex Revised: May 4, 2011 environmental samples or for differentiating between the total Published: May 18, 2011 r 2011 American Chemical Society 5294 dx.doi.org/10.1021/es1043084 | Environ. Sci. Technol. 2011, 45, 5294–5300 Environmental Science & Technology ARTICLE positive cytotoxicity and genotoxicity have been reported for the consisting of amino-functionalized derivatives of cyclodextrins β γ water-soluble C60 aggregates (nC60) despite its low hydro- designated as: -CD-NH2 1 and -CD-NH2 2 (Supporting phobicity.8 Information (SI) Figure 1A). The synthesis of these derivatives The first step to a better understanding of the fate and utilized previous literature procedures with slight modifica- transport of fullerenes and other nanomaterials is to develop tions:16 Briefly, 0.72 g of either β-CD or γ-CD was treated with reliable metrology and analytical sensors. These offer novel 1.2 g toluene-2-sulfonyl chloride, TsCl (Sigma-Aldrich) and screening and monitoring approaches toward a better under- ethylenediamine(1 mL)(Sigma-Aldrich, US) in 20 mL pyridine standing of engineered nanomaterials. Nanosensors can be (Sigma-Aldrich) and the mixture was refluxed for 7 h resulting in fi 1,9 β classi ed under two main categories: (i) Nanotechnology- yellow solids. The yellow solids were designated as -CD-NH2, 1 γ enabled sensors or sensors that are themselves nanoscale or have or -CD-NH2 2. These synthetic products (1 and 2) were stored nanoscale materials or components, and (ii) Nanoproperty- under ultra high purity nitrogen (UHP) until they were utilized quantifiable sensors. Nanomaterials dimensions are on the same for the immobilization onto the QCM surface. scale as biomolecules, which unveils exciting possibilities for their Successful synthesis of 1 and 2 were confirmed by 1HNMR interaction with biological species, such as microbial, tissue, cells, spectra recorded on a Bruker AM 360 spectroscopic system antibodies, DNA, and other proteins. Type I sensors have been equipped with 8.45 T magnet and multinuclear and inverse ° used for the construction of enzyme sensors, immunosensors, detection capabilities at 360 MHz at 20 C using D2O solvent (SI and genosensors, to achieve direct wiring of enzymes and relative Figure S1B). The 1HNMR sample concentrations were approxi- components to electrode surface, to promote spectroelectro- β β γ γ mated as 25 mg/mL of -CD, -CD-NH2 1, -CD and -CD- chemical reaction, to impose barcode for biomaterials and to 10,11 NH2 2. Compound 1, showed characteristic NH2 and methylene amplify signal of biorecognition event[. Extensive research protons with chemical shifts at δ ∼2.2 ppm and δ ∼3.0 papers and reviews using nanomaterials for chemical and bioas- ppm respectively. Compound 2 showed similar chemical shifts says have since been published.1,5 δ ∼ at 2.2 and 2.8 ppm for NH2 and methylene protons Despite the enormous literatures, there are few sensors to respectively (data not included). Chemical shifts from both measure nanoscale properties or sensors belonging to Type II. compounds 1 and 2 were consistent with the calculated theore- This class of nanosensors is an area of critical interest to tical chemical shifts values using ChemDraw for NH2 and CH2- nanotoxicology, detection and risk assessment, as well as for protons (δ = 2.0 and δ = 2.8 ppm respectively). These results monitoring of environmental and/or biological exposures to were consistent with literature precedence.12,16,17 In addition, nanomaterials such as fullerene C60. This is important because this modification is not only important for the immobilization engineered fullerenes C which are prepared via thermal reac- 60 chemistry but also for the enhanced cyclodextrin guestÀhost tions always exist as a mixture of C ,C and higher homo- 60 70 activity. For example, the depth of the cavity is extended from logues. While supramolecular complexation with hostÀguest À 0.78 to 1.10 nm and the hydrophilic nature of both ends of the β- recognition is a well-studied topic,12 14 and nanomaterials have CD cavity is changed due to the methyl groups attached to the been widely reported as components of sensing or other O-2, O-3, or O-6 of the cyclodextrin.18 Current work does not applications, to the best of our knowledge, there has neither ff fi been fullerene sensors reported nor the assembly of β-CD include studies on the e ect of the cyclodextrin modi cation or did not eliminate the role of such chemistry in the sensor achieved onto mass selective transducers for C60 nanoparticle sensing applications. This paper presents the development of fabrication. Category II nanosensor for the isolation and quantitative ana- Cyclodextrin Assembly onto the QCM Transducer. Com- lyses of engineered fullerene C while excluding other structur- pounds 1 and 2 were immobilized separately on QCM via the 60 DCC/NHS chemistry (Sigma-Aldrich).15 First, QCM was ally similar fullerenes C70 and higher homologues. cleaned in Piranha solution (H2SO4:H2O2 = 3:1, v/v) to remove ’ any organic impurities and rinsed in copious amount of ethanol/ EXPERIMENTAL SECTION water (1:1, v/v) mixture and dried gently in a stream of nitrogen. The cleaned QCM was subjected to the procedure shown in SI Microgravimetric Measurements. Microgravimetric mea- 0 surements were performed following a conventional Figure S1C. Briefly, the QCM was soaked for 1 h in 1 mM 3, 3 procedure.15 Briefly, all microgravimetric QCM experiments dithiopropionic acid, DTPA (Sigma-Aldrich) in acetone to were performed using a QCA 917-quartz crystal analyzer facilitate the formation of the sensor molecular configuration (Seiko EG&G). This was an open circuit system where only hereby designated as QCM (Au)-S-(CH2)2-COOH acid 3. The the gold-coated quartz crystal (QA-A9M-Au(M)) from Ad- QCM with immobilized acid was rinsed again to remove any μ vanced Measurement Technology (Oak Ridge, TN) working unreacted DTPA and then soaked in a mixture of 400 Lof 2 μ ∼ electrode (QCM, area ∼0.2 cm ) was connected in the absence 5 mM DCC (in acetone) plus 400 Lof 5.0 mg/mL (in water) β γ μ of the auxiliary and the reference electrodes.). The resonators either -CD-NH2 1 or -CD-NH2 2.