9.2 Nanoparticle deposition studies using a quartz crystal  (Page 2/3)

The applications of the QCM-D ranges from the deposition of nanoparticles into a surface, from the interaction of proteins within certain substrates. It can also monitors the bacterial amount of products when feed with different molecules, as the flexibility of the sensors into what can be deposited in them include nanoparticle, special functionalization or even cell and bacterias!

Experimental planning

In order to use QCM-D for studing the interaction of nanoparticles with a specific surface several steps must be followed. For demonstration purposes the following procedure will describe the use of a Q-Sense E4 with autosampler from Biolin Scientific. A summary is shown below as a quick guide to follow, but further details will be explained:

1. Surface election and cleaning according with the manufacturer recommendations.
2. Sample preparation including having the correct dilutions and enough sample for the running experiment.
3. Equipment cleaning and set up of the correct parameters for the experiment.
4. Data acquisition.
5. Data interpretation.

Surface election

The decision of what surface of the the sensor to use is the most important decision to make fore each study. Biolin has a large library of available coatings ranging from different compositions of pure elements and oxides ( [link] ) to specific binding proteins. It is important to take into account the different chemistries of the sensors and the results we are looking for. For example studying a protein with high sulfur content on a gold sensor can lead to a false deposition results, as gold and sulfur have a high affinity to form bonds. For the purpose of this example, a gold coated sensor will be used in the remainder of the discussion.

Sensor cleaning

Since QCM-D relies on the amount of mass that is deposited into the surface of the sensor, a thorough cleaning is needed to ensure there is no contaminants on the surface that can lead to errors in the measurement. The procedure the manufacturer established to clean a gold sensor is as follows:

1. Put the sensor in the UV/ozone chamber for 10 minutes
2. Prepare 10 mL of a 5:1:1 solution of hydrogen peroxide:ammonia:water
3. Submerge in this solution at 75 °C for 5 minutes.
4. Rinse with copious amount of milliQ water.
5. Dry with inert gas.
6. Put the sensor in the UV/ozone chamber for 10 minutes as shown in [link] .

Once the sensors are clean, extreme caution should be taken to avoid contamination of the surface. The sensors can be loaded in the flow chamber of the equipment making sure that the T-mark of the sensor matches the T mark of the chamber in order to make sure the electrodes are in constant contact. The correct position is shown in [link] .

Sample preparation

As the top range of mass that can be detected is merely micrograms, solutions must be prepared accordingly. For a typical run, a buffer solution is needed in which the deposition will be studied as well as, the sample itself and a solution of 2% of sodium dodecylsulfate [CH ₃ (CH ₂ ) ₁₀ CH ₂ OSO ₃ Na, SDS]. For this example we will be using nanoparticles of magnetic iron oxide (nMag) coated with PAMS, and as a buffer 8% NaCl in DI water.