A decoloration/recoloration cycling-associated photo-stimulated fuel cell to assess potential health risks caused by TiO2 nanoparticles and tris(hydroxymethyl)aminomethane

https://doi.org/10.1016/j.jelechem.2020.114126Get rights and content

Highlights

  • A decoloration/recoloration cycling-associated photo-stimulated fuel cell is built.

  • Photo-physical measurements suggest formation of TiO2@MB-BSA hybrids.

  • Color retention efficiency/photocurrent are able to evaluate BSA photodamage.

  • TiO2, MB and Tris synergistically increase photo-oxidative damage of BSA.

  • This study shows new approaches to assess the increased hazards to human health.

Abstract

Nano-sized TiO2 and tris(hydroxymethyl)aminomethane (Tris) are widely used in diverse commercial products such as cosmetics, medicines and paints, therefore their possible exposure and consequent risk to humans and natural environments rouse public concerns. This paper evaluates potential health risks of UV-excited TiO2 and Tris buffer by constructing a decoloration/recoloration cycling-associated photo-stimulated fuel cell and using methylene blue (MB) as a color indicator through photo-oxidative damage of bovine serum albumin (BSA). Nano-TiO2 can bind BSA and MB to form TiO2@BSA-MB hybrids, revealed by TiO2-tuned binding constant, fluorescence quenching constant and MB-induced BSA configuration transition. The color retention efficiencies after decoloration/recoloration cycling and photocurrent responses from photo-stimulated fuel cells are able to monitor the photo-oxidative damage to BSA. Furthermore, Tris can be oxidized in photo-stimulated fuel cells in the absence of BSA whereas BSA has ability to depress the photocatalytic oxidation of Tris, which is found to increase the photo-oxidative damage of BSA caused by TiO2 and MB, therefore the simultaneous presence of TiO2, MB and Tris synergistically increases the photo-oxidative damage of BSA. The present results show new approaches for assessing the increased hazards to human health caused by photoradiation, nanomaterials and organic additives.

Introduction

With increasing applications of manufactured nanoparticles in diverse commercial products including cosmetics, medicines and paints, their possible exposure and consequent risk to humans and natural environments rouse public concerns [1,2]. Nano-sized titanium dioxide (TiO2) is one of most commonly used metal oxide nanoparticles. When nano-TiO2 is used as an inorganic filter in sunscreens against UV radiation, it possibly appears on skins and in swimming pools [3,4], and has potential to produce cytotoxicity, oxidative stress, and DNA, nerve and/or brain damages through penetrating skins and travelling blood vessels [[5], [6], [7], [8]]. Because nano-TiO2 always emerges in organic compound-containing systems [9,10], it is necessary to investigate the co-effects of TiO2 and organic additives on human health, especially upon incorporation of UV light.

Methylene blue (MB) has a long history of diverse applications [[11], [12], [13], [14], [15], [16]]. Firstly, MB is a thiazine dye that is brightly blue in an oxidizing environment and is reduced to colorless leucomethylene blue (LMB) in the presence of TiO2 and UV light. It was a signal indicator for the determination of oxygen while employing TiO2 nanocrystals as photosensitizers, and nonionic polymers as electron donors [17]. On the other hand, MB acted as redox mediators to realize paired photoelectrocatalytic reactions of glucose under nitrogen atmospheres [18], and to promote oxygen reduction with the assistance of Cu2O [19]. Secondly, as a heterocyclic aromatic compound, MB also was an indicator for the determination of biomolecules such as protein and nucleic acid [20,21]. Thirdly, MB showed biological membrane permeability, and high solubility in both water and organic solvents [22], therefore, it can be used in clinical medicine for treating methemoglobinemia [23], photodynamic therapy [24] or Alzheimer's diseases [25,26]. Fourthly, a low concentration of MB exhibited free radical scavenging activity, and therefore was regarded as a promising agent in anti-aging cosmetics [27]. Just for wide applications of MB, it may be exposed to natural and urban environments [28,29], and produce cytotoxic or anti-oxidative activities [30], especially in the presence of nano-TiO2 [31]. On the other hand, tris(hydroxymethyl)aminomethane (Tris) is often used as a buffer, medicine and/or neuroactive chemical in biological model systems [32,33], as a probe for assessing the photocatalytic activity of TiO2 using excitation light sources of 365 nm [34], and as a reducing agent in photocatalytic fuel cells employing TiO2 nanotubes-based photoanode and air-breathing enzymatic biocathode [35]. Additionally, serum albumin is the most abundant protein in blood plasma of all vertebrates, and its oxidative damage is involved in aging and age-associated neurodegenerative diseases [36,37]. Therefore, in the current work, an effort is made to study the protein photodamage caused by TiO2, MB and Tris.

The protein damage against exogenous substances has been widely investigated using various techniques including fluorescence spectroscopy [38], absorption spectroscopy [39], high-performance liquid chromatography [40], mass spectrometry [41], differential scanning calorimetry [42], capillary zone electrophoresis [43], and electrochemical methods [44,45]. In comparison, the spectral or electrochemical technique has attracted much attention due to its quick response and easy operation [46], and photo-stimulated fuel cell techniques have an advantage of more directly demonstrating the effects of semiconductor photosensitizers, redox mediators and reducing or oxidizing species on the protein photodamage [47,48]. Therefore, in this study, a decoloration/recoloration cycling-associated photo-stimulated fuel cell is constructed for rationally evaluating the co-effects of nano-TiO2, MB and Tris via photo-oxidative damage of serum proteins. Consider the fact that bovine serum albumin (BSA) has advantages of low cost, rich source and high homology degree with human serum albumin (HSA), it acts as model protein for the study on serum protein damage [49,50]. Fortunately, the color retention efficiencies after decoloration/recoloration cycling and photocurrent responses from photo-stimulated fuel cells are suitable for monitoring the photo-oxidative damage of BSA. It is the first time to find that the simultaneous presence of TiO2, MB and Tris largely increases the hazards to human health in the presence of UV radiation.

Section snippets

Chemicals and materials

Bovine serum albumin (BSA) was purchased from Qiyun Bio-technique Co., Guangzhou, China, L-tryptophan (Trp) from Qisheng Biotechnique Co., Guangzhou, China, and methylene blue (MB) from Damao Chemical Reagent Factory in Tianjin, China. The structures of MB and leuco-methylene blue (LMB) were shown in Fig. 1. Tris(hydroxymethyl)aminomethane (Tris) from Sigma was used either as an organic additives or as a buffer. Unless otherwise specified, 0.1 mol L−1 NaCl prepared with doubly distilled water

Photo-oxidative damage of BSA caused by MB and TiO2

Absorption spectra of MB and TiO2 in the absence and presence of BSA in Fig. 2 indicate that the UV irradiation of 15 min under an aerobic condition allows the original blue color of MB to be bleached by 67.2%, and to produce the colorless leuco-methylene blue (LMB). After turning off the light for 45 min, the LMB is re-oxidized into MB and a recoloration process is observed. Because MB is usually taken as the degradation model, and is photocatalytically decomposed in the

Conclusions

A decoloration/recoloration cycling-associated photo-stimulated fuel cell has been successfully built to evaluate the potential risks of TiO2, MB and Tris buffer using photo-oxidative damage of BSA. The TiO2-tuned binding constant and fluorescence quenching constant and MB-induced BSA configuration transition suggest the formation of TiO2@BSA-MB hybrids. The color retention efficiencies after decoloration/recoloration cycling and photocurrent responses from photo-stimulated fuel cells can be

CRediT authorship contribution statement

Yuwei Zhang: Investigation, Writing - original draft. Nanxi Li: Conceptualization, Software. Ziqiao Yan: Data curation. Gengxin Hu: Methodology. Hong Li: Supervision, Validation, Writing - review & editing.

Declaration of competing interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgments

This work was supported by the National Natural Science Foundation of China (No. 21271075).

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