Abstract

Solar Hunter is an artificial hydrogen production system comprising biofilm-anchored semiconductor nanorods (NRs) which efficiently convert photons to electrons, and engineered strain expressing [FeFe] hydrogenase that can efficiently catalyze Hydrogen production upon receiving the electrons donated by NRs. The success of this integrative hydrogen-producing system relies on robust construction and functional characterization of each part separately. We have proved that we successfully constructed and characterized our parts, as revealed below.

Detailed Proof

a. We, first, need to obtain a suitable nanomaterial, CdS, that absorbs solar energy and convert it into electrons. The detailed synthesis and characterization data is shown in our webpage Nanomaterials Session for further information. Some key data are reproduced below.

Synthesis and Characterization

Results

Synthesis and Characterization of CdS Nanorods

We synthesized CdS nanorods following a procedure adapted from a previously published protocol[1]. The synthesis procedure mainly contains two steps: synthesis of CdS seeds, followed by growth of CdS nanorods using CdS nanoparticles as nuclei.

Figure 3. Solutions of CdS nanoparticle seeds in TOP (left), CdS NRs in toluene (right)

Characterization of UV-Vis was performed to calculate the concentration of CdS seed in TOP solution and CdS nanorod in toluene solution. Also, PL spectrum of CdS NRs in toluene was collected to investigate the emission attribute of the nanorod. TEM image of the nanorods was acquired to study the shape and size distribution.

Figure 4. Result of CdS NRs ligand exchange experiments.

A ligand exchange experiment was performed and the result is shown in Figure 4

Figure 5. UV-Vis spectra of CdS seeds in TOP (A) and CdS nanorods in toluene (B);. Photoluminescence Spectrum of CdS nanorods in toluene (C).

The concentration of CdS seeds and CdS NR products were determined by using the UV-Vis spectrometer (Fig. 5 A, B). The peak shown in PL spectrum (Fig. 5 C) matches the absorption peak of the UV-Vis spectra, which thus proves the synthesis of CdS NRs.

Figure 6. TEM images of CdS NRs (A) and size distribution of CdS NRs (B). Note: 100 NRs in total were measured to determine the size distribution. The NRs thus measured have an average diameter of 3.93±0.57nm and average length of 66.81±6.74nm.

TEM confirms that synthesized products show nanorod feature, with an average diameter of 3.93±0.57nm and average length of 66.81±6.74nm.

b. To allow easy recycling of precious semiconductor nanomaterials, we utilized engineered biofilms to anchor nanomaterials via metal coordination chemistry. Please refer to Biofilm Session for the successful construction and characterization of engineered biofilms that allow firm binding of nanomaterials.

c. Finally, high-activity hydrogenase is necessary for our system. To achieve efficient enzymatic activities, we codon-optimized and constructed the whole hydrogenase gene clusters (from Clostridium Acetobutylicum) by leveraging the multi-expression Acembl System. Please refer to Hydrogenase Session for more details.

Main points we achieved in our project

1. Successful synthesis and characterization of CdS NRs and CdSe QDs with desired features.

2. Successful production and characterization of Biofilms, and proved demonstration that engineered biofilms composed of CsgA-Histag fused protein allowed firm binding of semiconductor nanomaterials. BioBrick BBa_K2132001

3. Successful construction and sequence of [FeFe]-hydrogenase gene clusters from Clostridium acetobutylicum and integrate all genes into one single plasmid to allow reliable expression.

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 <img src="https://static.igem.org/mediawiki/2016/e/eb/T--ShanghaitechChina--fc.png" style="width:75%;">
 <figcaption >
-<p class="cap"><b>Figure 2.</b> The flow chart for synthesis and characterization of nanomaterials.</p>
-</figcaption></div>
-</center>
-<h3 class="bg"><b>Methods</b></h3>
-<p><b class="bg">Ligand Synthesis and Exchange:</b></p><p>
-To increase the solubility and enable selective binding ability of the nanomaterials, the lipophilic ligands of our synthesized nanomaterials should be replaced by special ligands through ligand exchange. We used a well-developed procedure (developed in Zhong Lab@ShanghaiTech) to synthesize this ligand. We performed the ligand exchange experiment to replace the origin ligand of the nanomaterials. The result of ligand exchange experiment was shown by the following image. After this experiment, the nanomaterials were ready to be harnessed as the binding material of the biofilm and the solar energy harvester of the Solar Hunter.</p><p></p>
-<p><b class="bg">Ultraviolet-visible (UV-Vis) spectroscopy:</b></p><p>
-The Ultraviolet-visible (UV-Vis) spectroscopy is an absorption spectroscopy in the near-UV and visible spectral region. The UV-Vis spectroscopy is normally used as a quantitative and qualitative characterization for different analytes. As QDs and NRs solutions contain large amount of transition metal irons, they exhibit absorption in UV-Vis range due to stimulated transision. And after determined the molar absorptivity(ε) from the concentration of Cd<sup>2+</sup>, the molarity can be calculated by the following equation: </p><center><p></p><p>A=εBC</p></center><p></p><p>In the equation, A(Abs) refers to absorption; ε(Abs*cm<sup>-1</sup>*M<sup>-1</sup>) refers to molar absorptivity; B(cm) refers to the length of cuvette; C(M) refers to the molarity of the QD or NR solution.The UV-Vis spectrometer we use is Agilent Cary 5000.</p><p></p>
-<p><b class="bg">Photoluminescence(PL) spectroscopy:</b></p><p>
-The Photoluminescence(PL) spectroscopy is a widely used tool for characterization of electronic and optical properties of analytes, especially quantum dots and nanorods. Briefly, the PL spectroscopy detects photon emitted in a certain spectral region when the samples are excited by light at a certain wavelength. The PL spectroscopy can be used to determine the excitation peak and emission peak. The position of the emission peak can indicate whether the synthesis of QDs and NRs is successfully performed. The best excitation wavelength and the best emission wavelength, which are of great importance for utilizing the use of QDs and NRs as characterization tools, can also be known from the position of the peaks. The PL spectrometer we use is HORIBA FL-3.</p><p></p>
-<p><b class="bg">Transmission Electron Microscope(TEM):</b></p><p>
-Transmission Electron Microscope (TEM) was used to image the shapes and sizes of QDs and NRs. The 120KV TEM (National Protein Facility Center, Shanghai, China) we used provides the resolution of around 0.2nm. The TEM sample of our lipophilic QDs and NRs solution is prepared by simply dropping 10 μL of the solution on to the copper grid.</p><p></p>
 <h3 class="bg"><b>Results</b></h3>

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Revision as of 01:19, 19 October 2016