Tuning the band gap of ferritin nanoparticles by co-depositing iron with halides or oxo-anions

Abstract

ARTICLE This journal isIron-containing ferritin has been used for light harvesting and as a photocatalyst. In this study, we test the hypothesis that changing the iron mineral core composition can alter the light harvesting and photocatalytic properties of ferritin, by co-depositing iron in the presence of halides or oxo-anions. This caused the anions to be incorporated into the iron mineral. We report that some of these new iron minerals possess different band gaps than the original ferrihydrite within ferritin. We found an increase in band gap of up to 0.288 eV or a decrease by as much as 0.104 eV, depending on the type of anion and amount of anions incorporated into the ferrihydrite mineral. ARTICLEThis journal is

Permanganate-based synthesis of manganese oxide nanoparticles in ferritin

“…In order to determine the effect of MnO 4on Mn loading into ferritin, we first prepared apoferritin through dialyzing horse spleen ferritin against thio-glycolic acid. This removes the ferrihydrite core and readies the ferritin for metal loading [27,36]. Reaction solutions were prepared by adding 3.0 mg (6.67 nmol) of apoferritin to 1.0 ml of one of the following three buffered solutions: 1 M pH 5.4 2-(N-morpholino) ethanesulfonic acid buffer, 1 M pH 7.4 imidazole buffer, or 1 M pH 9.4 N-(1,1-Dimethyl-2-hydroxyethyl)-3-amino-2hydroxypropanesulfonic acid buffer.…”

“…Using oxygen or hydrogen peroxide as the oxidant has allowed for the synthesis of many different nanoparticles in ferritin [22,[25][26][27]. The protein shell is also known to allow diffusion of oxo-anions [27,[36][37][38][39][40][41] and divalent metals [42][43][44][45][46] into the ferritin cavity. Metal oxoanion minerals can thus be deposited inside ferritin by adding oxo-anions to the reaction buffer during iron loading [27,36].…”

“…The protein shell is also known to allow diffusion of oxo-anions [27,[36][37][38][39][40][41] and divalent metals [42][43][44][45][46] into the ferritin cavity. Metal oxoanion minerals can thus be deposited inside ferritin by adding oxo-anions to the reaction buffer during iron loading [27,36]. Using these methods, Mn nanoparticles have previously been formed inside of ferritin [3,21,22].…”

“…Many nanoparticles formed in ferritin act as semiconducting materials [47,48], and band gap energies for some previously synthesized nanoparticles have been reported, including indirect and direct transitions for Co-, Mn-, and Ti-oxyhydroxides [3] and in nanoparticles where the native Fe(O)OH has been co-deposited with PO , [27]. In the latter paper, Smith et al also observed that ferritin iron loading in the presence of MnO 4produces a core containing both iron and manganese [27]. This observation indicates a possible new route for manganese loading into ferritin, where MnO 4may be able to replace oxygen as the oxidant and subsequently be incorporated into the ferritin core.…”

Tuning Ferritin’s band gap through mixed metal oxide nanoparticle formation

“…As such, there are only a few cases where these minerals have been recorded in ferritin. In these instances, the cores formed contain both Fe and Mn and were formed by introducing both metals in a low oxidation state to the apoferritin molecule [5,15].…”