Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy 136 (2015) 1607–1613

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Fluorescent reversible regulation based on the interactions of topotecan hydrochloride, neutral red and quantum dots Linlin Wang a, Yizhong Shen a, Shaopu Liu a, Jidong Yang a,b, Wanjun Liang a, Dan Li a, Youqiu He a,⇑ a b

Key Laboratory on Luminescence and Real-Time Analysis, Ministry of Education, School of Chemistry and Chemical Engineering, Southwest University, Chongqing 400715, PR China School of Chemical and Environmental Engineering, Chongqing Three Gorges University, Chongqing, Wanzhou 404000, PR China

h i g h l i g h t s

g r a p h i c a l a b s t r a c t

 Interactions of topotecan

hydrochloride, neutral red and quantum dots were studied.  Research on the reaction mechanisms were performed by various optical measurements.  The results were good for achieving the controlling of the fluorescent reversible regulation of QDs.

a r t i c l e

i n f o

Article history: Received 20 June 2014 Received in revised form 30 September 2014 Accepted 15 October 2014 Available online 24 October 2014 Keywords: Quantum dots Topotecan hydrochloride Neutral red Fluorescence

a b s t r a c t The interactions of topotecan hydrochloride (THC), neutral red (NR) and thioglycolic acid (TGA) capped CdTe/CdS quantum dots (QDs) built a solid base for the controlling of the fluorescent reversible regulation of the system. This study was developed by means of ultraviolet–visible (UV–vis) absorption, fluorescence (FL), resonance Rayleigh scattering (RRS) spectroscopy and transmission electron microscopy (TEM). Corresponding experimental results revealed that the fluorescence of TGA-CdTe/CdS QDs could be effectively quenched by NR, while the RRS of the QDs enhanced gradually with the each increment of NR concentration. After the addition of THC, the strong covalent conjugation between NR and THC which was in carboxylate state enabled NR to be dissociated from the surface of TGA-CdTe/CdS QDs to form more stable complex with THC, thereby enhancing the fluorescence of the TGA-CdTe/CdS QDs-NR system. What is more, through analyzing the optical properties and experimental data of the reaction between TGA-CdTe/CdS QDs and NR, the possible reaction mechanism of the whole system was discussed. This combination of multiple spectroscopic techniques could contribute to the investigation for the fluorescent reversible regulation of QDs and a method could also be established to research the interactions between camptothecin drugs and dyes. Ó 2014 Elsevier B.V. All rights reserved.

Introduction Topotecan hydrochloride (THC) is a soluble analogue of camptothecin (CPT) which is extracted from the fruits and leaves ⇑ Corresponding author. Tel.: +86 23 68367475; fax: +86 23 68254000. E-mail address: [email protected] (Y. He). http://dx.doi.org/10.1016/j.saa.2014.10.054 1386-1425/Ó 2014 Elsevier B.V. All rights reserved.

of camptotheca acuminata decne [1–3]. According to previous researches, THC and other CPT derivatives in a dissolved state would engender a hydrolysis of the ring lactone to form a carboxylate [4,5]. The ring opening process of THC was as shown in Fig. 1(A), and the open-loop structure had little pharmacodynamic effects for it becomes non-active state. All of theses implied the

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potential usefulness of developing a method to investigate the character of THC which was in carboxylate state. Neutral red (NR) is a weak alkaline indicator and an alkaline cells in vivo phenazine dye staining. Because of its photoactive, NR has been used as an acid-base indicator, adsorbing agent and redox indicator. Neutral red mainly exists in the forms of HNR+ and NR in weak alkaline aqueous solution. The ionization shift of neutral red was shown in Fig. 1(B). Modification of the nanocluster surfaces with photoactive dyes molecules enhances the photochemical activity, and renders the organic–inorganic nanohybrid materials suitable for optoelectronic applications [6]. This effect phenomenon can meet the further investigation requirements of the adsorption behavior of dye molecules on the surface of nanoparticles [7]. As colloidal semiconductor nanocrystals, quantum dots (QDs) have attracted the attentions of many researchers in recent years. In comparison to organic dyes and fluorescent proteins, QDs have unique functional and structural properties, such as small size, high fluorescence quantum yields, large absorption cross sections, narrow and Gaussian emission spectra, size- and compositiontunable emission and high photobleaching threshold [8,9]. Earlier studies related to the interactions between QDs and some compounds, for instance, the interactions with vitamin B12 [10], hemoglobin [11] and melamine [12] had revealed that the reactions would change the photophysical properties of QDs [13,14]. In this article, the interactions among THC, NR and TGA-CdTe/ CdS QDs were investigated by UV–vis absorption, FL and RRS spectroscopy. Through analyzing the corresponding experimental phenomena, NR could produce a prominent quenching effect on the original fluorescence and a significant enhancing effect on the RRS intensity of TGA-CdTe/CdS QDs. After the addition of THC, the fluorescence intensity of the TGA-CdTe/CdS QDs-NR system would be enhanced proportional with the each increment of THC, what probably for the reason of strong covalent conjugation between NR and THC which was in carboxylate state. The quenched fluorescence of TGA-CdTe/CdS QDs was due to the formation of non-fluorescent complex attached to the surface of the QDs which generating from the interaction between NR and the QDs. As the strong covalent conjugation ability that occured between THC and NR in the system might enable the non-fluorescent complex to be dissociated from the surface of TGA-CdTe/CdS QDs, the fluorescence intensity of TGA-CdTe/CdS QDs-NR system could be enhanced. Accordingly, it could be able to control the fluorescent reversible regulation of TGA-CdTe/CdS QDs effectively and the spectral change of the system played a guiding role for

Fig. 1. (A) The ring opening of THC; and (B) the ionization shift of NR.

the investigation of the interactions between camptothecin drugs and dyes. Experimental Apparatus Steady-state fluorescence spectra were recorded by a Hitachi F2500 spectrofluorophotometer (Hitachi Company, Japan) with a xenon lamp used for excitation at room temperature. The absorption spectra were recorded by making use of a UV-2450 spectrophotometer (Tianmei Corporation, Shanghai, China). JEOL JEM-2100 transmission electron microscopy (TEM, Hitachi, Japan) was used to observe the appearance and size of nanoparticles. The pH values of the aqueous solutions were measured though utilizing a PHS-3C pH meter (Leici, Shanghai, China). Materials and reagents In present study, the principal chemical reagents adopted were CdCl22.5H2O (Shanghai Chemicals Reagent Co., Shanghai, China), Te powder (Sinopharm Chemical Reagent Co., Shanghai, China), NaBH4 (Tianjin Huanwei Fine Chemical Co., Tianjin, China). Thioglycolic acid (TGA), neutral red (NR) and all of the amino acids used in this paper were purchased from Aladdin Reagent Co. (Shanghai, China). Glucose, urea and albumin egg were obtained from Sigma (St. Louis, MO, USA). The solutions were buffered with phosphate buffer solution (PBS), which was prepared by dissolving 1/30 mol L1 KH2PO4 and 1/30 mol L1 Na2HPO4 together in certain percentage. Unless stated, all the chemicals were of analytical reagent grade or better without any further purification. Deionized distilled water prepared from a water purification system was used throughout. Methods Synthesis of TGA-CdTe/CdS QDs Aqueous colloids of TGA-CdTe/CdS QDs solution were prepared according to the previously described methods [15,16]. With a slow Ar flow and the magnetic stirring, tellurium powder (Te, 0.0191 g) was reacted with excessive sodium borohydride in deionized water which were placed in a 50 mL three-necked flask. Gradually, the colorless solution of sodium hydrogen telluride (NaHTe) was prepared. CdCl22.5H2O (0.1370 g) was dissolved in 150 mL deionized water, 80 lL TGA as stabilizer was added under vigorous stirring and then the pH was adjusted to 11.0 by dropwise addition of 1.0 mol L1 NaOH solution. The solution was deaerated by Ar bubbling for about 30 min (min). With the slow Ar flow, the H2SO4 (0.5 mol L1) solution was then introduced to NaHTe to produce H2Te gas, which passed through the oxygen-free Cd2+ solution. At this stage, CdTe precursors were formed and the molar ratio of Cd2+/TGA/HTe was fixed at 1:2:0.25. After that, the resulting solution mixture was heated to 369 K for 1.8 h (h) under open-air condition with condenser. Then 1.0 mL thioacetamide solution which concentration was 4.05 mg mL1 was added into the as-prepared CdTe solution. The solution was heated to 369 K under open-air conditions and refluxed for another 1 h. Finally, yellow-emitting TGA-CdTe/CdS QDs were obtained. The concentration of TGA-CdTe/CdS QDs was dependent on the Te2 concentration [17]. Experimental procedure 1.0 mL as-prepared TGA-CdTe/CdS QDs, 1.0 mL PBS (pH = 7.6), and an appropriate amount of NR was dispersed in a 10 mL volumetric flask and then diluted with deionized water to the mark. The each increment of the added NR concentration (cNR) was

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0–2.4  105 mol L1. These samples were used for investigating the fluorescence quenching phenomena. In addition, the mixture which with the addition of 2.4  105 mol L1 NR was applied to analyze the fluorescence enhancement phenomena of TGA-CdTe/ CdS QDs-NR system by the introduction of THC which was in the concentration range of 0–15.26  106 mol L1. Furthermore, these two stage analysis processes were all needed incubation for 10 min at room temperature to obtain final fluorescence intensities. The resulting solutions were studied by analyzing the UV–vis absorption, FL and RRS spectroscopy [18]. Results and discussion Characterization of the synthesized TGA-CdTe/CdS QDs The TEM image which revealed the morphology and diameter of the aqueous TGA-CdTe/CdS QDs was as shown in Fig. 2. It was quite evident that the nanoparticles’ shape was approximately spherical and the sizes were uniform in diameter of about 3 nm. According to previous studies, a compressive CdS layer wrapped the nanocrystalline CdTe core which formed a lattice-mismatched type-II core/shell heterostructure QDs could acquire high-quality luminescent properties [19]. Thus, it was more reasonable to synthesize the UV–vis absorption and FL emission spectra of TGA-CdTe/CdS QDs. As shown in Fig. 3, the characteristic absorption peak of TGA-CdTe/CdS QDs was located at 562 nm and the excitonic absorption was strong. Since QDs had the property of size- and composition-tunable emission, the excitation wavelength of 288 nm was chose to obtain the apparent spectrum. Under the condition of excitation wavelength of 288 nm, the fluorescence spectrum of TGA-CdTe/CdS QDs demonstrated that the full width half maximum (FWHM, about 48 nm) was narrow and exhibited good symmetry, and the investigated fluorescence band was centered at 588 nm.

Fig. 3. UV–vis absorption (a) and fluorescence spectrum (b) of the TGA-CdTe/CdS QDs dispersed in water. The emission spectrum was obtained under excitation at 288 nm.

and the –COOH existed in its cationic form (–COO). As could be seen from the spectrum of neutral red (curve b), there was an absorption peak located at 535 nm, so it could be inferred that neutral red existed partly in HNR+ before it reacted with TGA-CdTe/CdS QDs. Under the experimental conditions, HNR+ could combine with –SCOO– through electrostatic force. Curve (a) was the UV–vis absorption spectrum of TGA-CdTe/CdS QDs with distilled water as the reference, and curve (d) was the UV–vis absorption spectrum of TGA-CdTe/CdS QDs with NR as the reference. By comparing curve (a) with curve (d), an obviously spectral change was presented, which implied there was a strong interaction between TGA-CdTe/CdS QDs and NR. Herein, the new absorption peak indirectly represented the formation of a new substance in this system.

UV–vis absorption spectra Through analyzing the UV–vis absorption spectroscopy, it is easy to comprehend the change of molecular structure. Neutral red is a phenazine dye, in weak alkaline aqueous solution mainly exists as the forms of HNR+ and NR, and the absorption peak of HNR+ appears at 535 nm and that of the NR appears at 452 nm [20]. As illustrated in Fig. 4, the UV–vis absorption spectra of TGA-CdTe/CdS QDs-neutral red system were discussed. As a stabilizer, TGA was connected on the surface of QDs by the Cd–S bond

Fluorescence spectra As a thiol-capping reagent, TGA played a significant role in the synthesis of TGA-CdTe/CdS QDs, and efficiently improved watersolubility and stability through forming a Cd–thiol complex around the surface of QDs. This complex layer occupied the surface sites and passivated the surface to maintain high-quality fluorescence emission [21]. However, NR acted as chelating reagents in this procedure and partly broken the particle layer, resulting in the formation of a new complex. Fig. 5 displayed the fluorescence emission spectra of TGA-CdTe/CdS QDs in the absence and presence of NR with varying concentrations under the optimum conditions. And the fluorescence intensity of separate THC solution was very weak. Obviously, the fluorescence quenching extent of TGA-CdTe/CdS

Fig. 2. TEM image of TGA-CdTe/CdS QDs.

Fig. 4. UV–vis absorption spectra of (a) TGA-CdTe/CdS QDs (with distilled water as the reference), (b) NR, (c) the mixture solution system (TGA-CdTe/CdS QDs and NR), and (d) TGA-CdTe/CdS QDs (with NR as the reference). The concentration of TGACdTe/CdS QDs was 0.8  104 mol L1, NR was 1.2  105 mol L1, and the volume of PBS buffer solution was 1.0 mL (pH = 7.6).

NR as an excellent quencher to TGA-CdTe/CdS QDs

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Fig. 5. Fluorescence spectra of TGA-CdTe/CdS QDs after the addition of different concentrations of NR, spectrum a–i: TGA-CdTe/CdS QDs-NR system (NR: 0, 0.3, 0.6, 0.9, 1.2, 1.5, 1.8, 2.1, 2.4  105 mol L1, respectively), and the curve j represented the fluorescence spectrum of THC (8.72  106 mol L1). The concentration of TGACdTe/CdS QDs was 0.8  104 mol L1, and the volume of PBS buffer solution was 1.0 mL (pH = 7.6). The inset showed the linearly change of the quenched fluorescence intensity of TGA-CdTe/CdS QDs (F0/F) against the different concentrations of NR.

QDs was directly proportional to the concentration of NR from 0 to 2.4  105 mol L1. When the concentration of NR was beyond 2.4  105 mol L1, corresponding fluorescence intensity variation was almost remained unchanged. Videlicet, the concentration of NR at 2.4  105 mol L1 could cause the fluorescence quenching degree of TGA-CdTe/CdS QDs to reach a limit. Meanwhile, by comparison, the wavelength emission maximum (kmax) of TGA-CdTe/ CdS QDs presented a 3 nm blue-shift (from 588 to 585 nm) at the higher NR concentration, which was due to the formation of TGA-CdTe/CdS QDs-NR complex [22]. This result mediately testified that the new generation of materials on the surface of TGACdTe/CdS QDs induced obvious fluorescence quenching. It is well known that the process of fluorescence quenching is usually divided into two categories, static quenching and dynamic quenching. Generally speaking, static quenching is due to the formation of non-luminous complex while dynamic quenching results from collision between quenching agent and fluorophor [23]. According to their differing dependence on temperature, they can be distinguished. The quenching constants increase with the increasing temperature for dynamic quenching, whereas the revers effect is observed in case of static quenching [24]. In a controlled experiment, to explore the mechanism of the reaction, the Stern– Volmer equation played an important role in revealing the quenching behavior of NR on the fluorescence intensity of TGA-CdTe/CdS QDs at different temperatures [25]:

F 0 =F ¼ 1 þ K sv ½Q

ð1Þ

Fig. 6. Stern–Volmer plots for the TGA-CdTe/CdS QDs-NR solution system at three different temperatures in PBS buffer solution. The concentration of TGA-CdTe/CdS QDs was 0.8  104 mol L1, and the volume of PBS buffer solution was 1.0 mL (pH = 7.6). The inset showed the change of the reaction between the Stern–Volmer quenching constants Ksv and temperature.

absorption and fluorescence spectra of the TGA-CdTe/CdS QDsNR system were changed, but also the RRS intensity. As illustrated in Fig. 7, the RRS intensity of separate THC solution (curve a) or TGA-CdTe/CdS QDs solution (curve b) was very weak. While TGA-CdTe/CdS QDs and NR were mixed together in PBS buffer solution (pH = 7.6), the RRS intensity of the system was significantly enhanced in the wavelength range of 220–700 nm and reached the maximum at 330 nm. RRS is an absorption-rescattering process produced by the resonance between the Rayleigh scattering and the light absorption with the same frequency when the wavelength of Rayleigh scattering is located at its absorption band [27,28]. According to Figs. 3 and 7, the contrast between the absorption spectrum of TGACdTe/CdS QDs and the RRS spectra of QDs-NR system indicated that the peaks located at 330 nm and 560 nm were situated in its absorption band, resulting in the enhancement of resonance scattering. In the neuter and weakly alkaline media, TGA could selfassemble on the surface of TGA-CdTe/CdS QDs to form negatively charged supermolecules. On the basis, the TGA-CdTe/CdS QDs and HNR+ could react to form the complex which was caused by the electrostatic attraction between them. Earlier studies had been reported that the volume increment of molecule was contributed to the enhancement of scattering intensity [29]. Namely, the complex formation between TGA-CdTe/CdS QDs and NR resulted in the increase of the molecular volume, which also gave rise to the enhancement of RRS intensity. Optimization of the reactions

In this formula, F0 and F were respectively the fluorescence intensities of TGA-CdTe/CdS QDs in the absence and presence of the quencher (NR), [Q] was the concentration of NR, and Ksv was the Stern–Volmer quenching constant. This equation (Eq. (1)) was applied to describe the linear regression Stern–Volmer plots of F0/F against [Q] at various temperatures (as shown in Fig. 6). Table 1 listed the diverse values of Ksv at the temperatures of 281, 289 and 297 K. As could be seen, the Stern–Volmer quenching constants were decreased with the increasing temperatures, which relationship between the two was inversely. It could be inferred that the possible quenching mechanism was static quenching rather than dynamic quenching, because of the formation of TGA-CdTe/CdS QDs-NR complex [26].

Effect of the acidity In accordance with the previous reports, the pH value of solution has a great influence on the fluorescence of QDs [30]. During this experiment, it not only had an effect on the NR-induced fluorescence quenching, but also the fluorescence recovery by THC. Herein, the effect of acidity on this system was studied from pH 7.0 to 8.0. At pH of 7.6, the fluorescence intensity of TGA-CdTe/ CdS QDs quenched by NR reached its maximum value, and the restored fluorescence caused by THC achieved its peak value simultaneously. The possible reason was the reaction in the system relatively more stable at about pH of 7.6 [31,32]. In order to get more significant results, the pH value of 7.6 was selected in this article.

RRS spectra To further explore the reaction mechanism of TGA-CdTe/CdS QDs with NR, the RRS spectra of the QDs-NR system was investigated, as well. Under optimum conditions, not only the UV–vis

Effect of concentration of TGA-CdTe/CdS QDs By the method of fixed parameters of the concentration of NR and the pH constant while changing the concentration of TGACdTe/CdS QDs, the accompanying fluorescent diversification of

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Table 1 Stern–Volmer quenching constants for the interaction of TGA-CdTe/CdS QDs with NR at different temperatures. Temperature (K) 281 289 297 a b

Sterm–Volmer linear equation 5

F0/F = 0.7738 + 4.822  10 [Q] F0/F = 0.6879 + 3.528  105 [Q] F0/F = 0.8257 + 2.374  105 [Q]

Ksv (L mol1) 5

4.822  10 3.528  105 2.374  105

Ra

S.D.b

0.9889 0.9822 0.9769

0.2282 0.2121 0.1628

R was the correlation coefficient. S.D. was the standard deviation for the Ksv values.

Fig. 7. RRS spectra of the TGA-CdTe/CdS QDs-NR system, spectrum b–j: TGA-CdTe/ CdS QDs-NR system (NR: 0, 0.4, 0.8, 1.2, 1.4, 1.6, 1.8, 2.0, 2.4  105 mol L1, respectively), and the curve a represented the RRS spectrum of THC (8.72  106 mol L1). The concentration of TGA-CdTe/CdS QDs was 0.8  104 mol L1, and the volume of PBS buffer solution was 1.0 mL (pH = 7.6).

Fig. 8. UV–vis absorption spectra of (a) NR (with distilled water as the reference), (b) THC, (c) the mixture solution system (NR and THC), (d) NR (with THC as the reference). The concentration of NR was 2.4  105 mol L1, THC was 8.72  106 mol L1 and the volume of PBS buffer solution was 1.0 mL (pH = 7.6).

QDs-NR system was analyzed. When the added concentration of TGA-CdTe/CdS QDs was beyond 0.8  104 mol L1, the value of DF remained almost unchanged. This phenomenon indicated that the optimum concentration of TGA-CdTe/CdS QDs was 0.8  104 mol L1. Effect of incubation time The effect of incubation time on the interactions between NR and TGA-CdTe/CdS QDs under room temperature was investigated. The results drawn from the analysis revealed that the reaction finished within 10 min and the fluorescence intensity of the system could remain almost unchanged within 60 min. So the time scale of 10 min was chosen as the detection time throughout this experiment. Interactions of TGA-CdTe/CdS QDs-NR complex ensemble with THC In order to deliberate on the reaction mechanism between NR and THC, the UV–vis spectra of this reaction were demonstrated in Fig. 8. From the comparison of line (a) and line (d) of Fig. 8, it could be inferred that, when combined with THC, the maximum absorption peak position of NR was unchanged, but the absorbance value was decreased slightly. The generating variation of NR characteristic absorption peaks was might due to the p–p⁄ transition that existed in its conjugated structure. NR (positively charged) could react with THC which was in carboxylate state through electrostatic attraction, leading to the p–p⁄ transition energy DE (DE = ELOMO–EHOMO) been affected. As shown in Fig. 9, the fluorescence intensity of TGA-CdTe/CdS QDs quenched by NR was gradually recovered with the increasing amount of THC. As displayed in the inset of Fig. 9, the relationship between the enhanced fluorescence intensity of TGA-CdTe/CdS QDs-NR system and the different concentrations of THC (from 0 to 15.26  106 mol L1) was linearly, which fitted the following regression equation: DF = 3.2167 + 134.023c (c: mol L1). In the

Fig. 9. Fluorescence spectra of TGA-CdTe/CdS QDs-NR system in the presence of different concentrations of THC, spectrum a–h: TGA-CdTe/CdS QDs-NR-THC system (THC: 0, 2.18, 4.36, 6.54, 8.72, 10.90, 13.08, 15.26  106 mol L1, respectively); The concentration of TGA-CdTe/CdS QDs was 0.8  104 mol L1, the concentration of NR was 2.4  105 mol L1 and the volume of PBS buffer solution was 1.0 mL (pH = 7.6). The inset showed the linearly change of the restored fluorescence intensity of TGA-CdTe/CdS QDs-NR system (DF = F0–F) against the different concentrations of THC.

Scheme 1. Schematic graph of the proposed mechanism of the TGA-CdTe/CdS QDsNR-THC system.

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Table 2 An effect of coexistent substances for TGA-CdTe/CdS QDs-NR-THC system (concentration of the QDs was 0.8  104 mol L1, concentration of NR was 2.4  105 mol L1, concentration of THC was 13.08  106 mol L1). Coexistence material +



K (Cl ) Mg2+ (SO2 4 ) L-cysteine L-methionine L-glutamic acid Glycine Urea

Concentration (105 mol L1) 16.10 9.97 9.90 8.04 8.16 15.99 19.98

Relative error (%) 1.79 +1.51 0.50 0.79 +4.44 0.93 +1.86

above relational expression, DF was the difference value of F (recovered fluorescence intensity of TGA-CdTe/CdS QDs-NR system in the presence THC) and F0 (fluorescence intensity of TGA-CdTe/ CdS QDs quenched by NR which was at the concentration of 2.4  105 mol L1), and c was the concentration of THC. Since the binding ability of NR and THC was stronger than the conjugation reaction between NR and TGA-CdTe/CdS QDs, a moderate amount of THC might destroy the TGA-CdTe/CdS QDs-NR complex, change the defect of the surface of QDs which damaged by NR and restored the fluorescence of QDs. There existed an apparent blue-shift (588–533 nm) of the max emission peak of QDs, indicating the surface of TGA-CdTe/CdS QDs was changed [33]. For either TGA-CdTe/CdS QD or THC was negatively charged, the added THC which was in carboxylate state was prone to combine with NR (positively charged) to form a new complex and move away from the surface of QDs. As the result of these, the interaction between NR and THC possibly blocked the NR quenching effect to the fluorescence of TGA-CdTe/CdS QDs, and restored the electron–hole of QDs, so as the fluorescence of the system could be recovered. Based on the above observations, the possible mechanism for the TGA-CdTe/CdS QDs-NR-THC system was exhibited briefly in Scheme 1.

+

Na (NO 3) NH+4 (SO2 4 ) L-isoleucine L-threonine L-aspartic acid Glucose Albumin egg

Concentration (105 mol L1)

Relative error (%)

14.12 18.18 9.11 10.07 9.15 6.06 120 lg mL1

+3.01 +4.09 3.23 +2.08 +4.23 +1.94 +3.23

the mechanism discussion, the TEM image, UV–vis absorption, FL and RRS spectroscopy were used for analyzing the reaction of the system in detail. Corresponding experimental results proved that the quenching effect of NR for TGA-CdTe/CdS QDs was static reaction and the strong binding ability of NR and THC made them to move away from the surface of the QDs through forming a new complex, which possibly resulting in the fluorescence restoring of the system. Concurrently, this reaction of TGA-CdTe/CdS QDs-NR-THC system might proceed steadily under the conditions of coexisting interfering substances. Our results threw light on the prospective probability of controlling the fluorescent reversible regulation of QDs and might be valuable for developing a novel spectroscopic method. Acknowledgements This work was supported by Chongqing Municipal Key tory on Luminescence and Real-Time Analysis, Southwest sity (CSTC, 2006CA8006) and the National Natural Foundation of China (No. 21175015) and all authors here their deep thanks.

LaboraUniverScience express

References

Effect of interferences The influences of interferences on the fluorescence of the TGACdTe/CdS QDs-NR-THC system were investigated by adding a series of interferential substances such as amino acid, metal ions, inorganic anions and organic matters (Table 2). In the case of coexisting substances, if they induced a relative error of equal to or less than ±5% on the fluorescence intensity variation of the TGA-CdTe/ CdS QDs-NR-THC system, they would be considered having no interference with the reaction system. Most of the amino acids, as listed in Table 2, did not put up a remarkable effect on the fluorescence intensity of the TGA-CdTe/CdS QDs-NR-THC system. The corresponding outcomes demonstrated that the metal ions including K+, Mg2+, Na+, and the inorganic anions containing Cl, SO2 4 , NO 3 , could be allowed at high concentration in the solution without obvious interference. Other organic matters, such as glucose, urea and albumin egg, have also been brought in the TGA-CdTe/ CdS QDs-NR-THC system, and the consequence illustrated that they have no prominent influence on the system. Apparently, the information exhibited that this reaction of the TGA-CdTe/CdS QDs-NR-THC system might proceed steadily under the conditions of coexisting interfering substances. Conclusion In summary, through utilizing between NR and THC which was TGA-CdTe/CdS QDs-NR-THC system, fluorescent reversible regulation

Coexistence material

the relatively high affinity in carboxylate state in the we successfully obtained the of TGA-CdTe/CdS QDs. In

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Fluorescent reversible regulation based on the interactions of topotecan hydrochloride, neutral red and quantum dots.

The interactions of topotecan hydrochloride (THC), neutral red (NR) and thioglycolic acid (TGA) capped CdTe/CdS quantum dots (QDs) built a solid base ...
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