Photoluminescence intensity enhancement in SWNT aqueous suspensions due to reducing agent doping: Inﬂuence of adsorbed biopolymer N.V. Kurnosov a , V.S. Leontiev a , A.S. Linnik a , O.S. Lytvyn b , V.A. Karachevtsev a,⇑ a B. Verkin Institute for Low Temperature Physics and Engineering, National Academy of Sciences of Ukraine, 47 Lenin Ave., 61103 Kharkov, Ukraine b V. Lashkaryov Institute of Semiconductor Physics, National Academy of Sciences of Ukraine, 41 Nayki Ave., 03028 Kyiv, Ukraine article info Article history: Received 30 January 2014 In ﬁnal form 10 April 2014 Available online 20 April 2014 Keywords: Exciton Luminescence Quantum yield Carbon nanotubes Reducing agent Nanobiohybrid abstract The inﬂuence of biopolymer wrapped around nanotube on the enhancement of the semiconducting single-walled carbon nanotube (SWNT) photoluminescence (PL) in aqueous suspension which increases due to the reducing agent dithiothreitol (DTT) doping effect was revealed. The greatest enhancement of PL was observed for SWNTs covered with double- or single stranded DNA (above 170%) and DTT weak inﬂuence was revealed for SWNTs:polyC suspension (45%). The magnitude of the PL enhancement depends also on nanotube chirality and sample aging. The behavior of PL from SWNTs covered with various polymers is explained by the different biopolymers ordering on the nanotube surface. The ordered polymer conformation on the nanotube weakens the reducing agent doping effect. The method of reducing agent doping of nanotube:biopolymer aqueous suspension can serve as a sensitive lumines- cent probe of the biopolymer ordering on the carbon nanotube and can be used to increase the sensitivity of luminescent biosensors. Ó 2014 Elsevier B.V. All rights reserved. 1. Introduction Single-walled carbon nanotubes (SWNTs) possess unique photophysical properties investigation of which extends our knowledge in the fundamental quasi-one-dimensional physics but also assists in fabrication of new nano-photonic devices [1–3]. Unlike organic ﬂuorophores, SWNTs are far more photosta- ble, their photoluminescence (PL) is characterized with low photo- bleaching and with opportunity to suppress photoblinking effects by manipulation of their dielectric environment [4]. In addition, PL from SWNTs has narrow spectral lines at room temperature without background [5]. The PL intensity and spectral position of bands corresponding to individual SWNTs are very sensitive to the environment [6], making possible such applications as SWNT-based chemical and biological sensors [1] as well as imaging applications [7] exploited in nanomedicine as emission from SWNTs is observed in the near-infrared (NIR) range, in which the tissue displays the transparency window. However, low quantum yield (QY) of SWNT PL (approx. 0.1% in water) (see Rev. [8] and refer. therein) is one of the main obstacles that restrain wide production of such sensors, photonic devices. Such low emission efﬁciency of SWNTs is attributed to the presence of nanotube bundles with metallic tubes [5], which quench luminescence, and tube defects, that act as traps for mobile excitons with the effective non-radiative channel [9,10]. Low QY of SWNT PL is also caused by the intrinsic low-lying optically forbid- den (‘‘dark’’) states [11–14]. Even after removing of nonemissive metallic nanotubes and residual bundles among isolated SWNTs, QY of nanotube PL in aqueous suspension remains weak (1%) [15]. In certain organic solvents SWNT PL is much brighter [16], however, the nanotube PL in water is required for any applications in vitro and in vivo (sensing [1], imaging applications [7], drug delivery [17]). A number of surfactants or polymers have been used in attempts to isolate individual nanotubes and to increase the PL intensity from dispersed SWNTs [5–10,15–22,25,27–30]. One of the routes in this direction is creation of the ordered structure of surfactants or polymers near nanotube surface to exclude water from the tube surface, molecules of which may facilitate non- radiative exciton decay pathways. Choice of the surfactant/ polymer or synthesis of new ones that may readily encapsulate ﬂuorescent SWNTs allows enhancing PL QY up to 20% [16]. To overcome the inﬂuence of ‘‘dark’’ exciton states on inefﬁcient QY of SWNT Y. Piao et al. [18] suggested the chemical creation of a new, optically allowed state that lies below the predicted energy levels of dark excitons. As a result, they obtained brightening of nanotube PL by a factor of up to 28 and demonstrated that the http://dx.doi.org/10.1016/j.chemphys.2014.04.006 0301-0104/Ó 2014 Elsevier B.V. All rights reserved. ⇑ Corresponding author. Tel.: +380 57 340 1595; fax: +380 57 340 3370. E-mail address: karachevtsev@ilt.kharkov.ua (V.A. Karachevtsev). Chemical Physics 438 (2014) 23–30 Contents lists available at ScienceDirect Chemical Physics journal homepage: www.elsevier.com/locate/chemphys