L5 AuNP & Biomedical Applications Flashcards
Re W6 Quiz 4
- List TWO reasons why gold nanoparticles (Au NP) have been extensively used for nanomaterials research in general
(2 marks)
- Easy to synthesise stable Au NPs (different shapes and sizes as well)
- Excellent Biocompatibility and biostability after appropriate modification
- Can be used for both imaging (different colours, good optical properties) and therapy (both photothermal and also drug/gene delivery)
- Good to visualise with electron microscopy (because of high electron density on surface) → easy to characterize the physical properties
- Easy to functionalize
- Define ‘plasmon’.
- Photon = ‘quantum’ or ‘package’ (a single unit) of light
- Plasmon = ‘Quantum’/‘unit’ of plasma/electron oscillation. (Need the underlined two ‘keywords’ in your answer for full 1 mark.)
- “Waves” of motion from oscillating, “floating” electrons ← OK
- Note: It’s not just restricted to the surface - we really only talk about the surface because it only occurs at the surface in the context of gold nanoparticles
- Which of the following sentences best describes the surface plasmon resonance effect?
(A) Surface electrons oscillate upon interacting with white incident light, resulting in the oscillation of charge
(B) Electron clouds around the surface of nanoparticles such as gold reflect certain wavelengths and absorb others
(C) The size of the gold NP influences the crystal lattice structure, and the light reflected is dependent on the crystal structure (false).
(D) Electrons move from the valence band to the conduction band upon interacting with incident light
(A) Surface electrons oscillate upon interacting with white incident light, resulting in the oscillation of charge → absorption of specific wavelengths.
Absorb lower wavelength → reflect higher wavelength and vice versa
Incorrect:
(B) Electron clouds around the surface of nanoparticles such as gold reflect certain wavelengths and absorb others (missing the oscillation)
(C) The size of the gold NP influences the crystal lattice structure, and the light reflected is dependent on the crystal structure (false)
(D) Electrons move from the valence band to the conduction band upon interacting with incident light (this mechanism similar to how quantum behave - where the ‘drop’ from the excited state to the ground of an electron results in the emission of photons of corresponding energy from that ‘drop’ ← oversimplification).
- Which of the following parameters does NOT dictate the colour emitted by a solution of gold nanoparticles?
(A) Separation distance between Au NP
(B) Size of Au NP
(C) Geometry of Au NP
(D) Amount of Au NP
(D) Amount of Au NP
Incorrect:
(A) “Separation distance between Au NP” - can lead to multiple peaks or aggregation (causing different colour to be emitted) ← this can be used as a mechanism for biosensing (i.e. aggregation in the presence of a specific biomolecule)
(B) “Size of Au NP” - larger NP → shift to larger wavelengths
As particles get larger, the absorption profile shifts towards the larger wavelengths (red-shift), and thus the solution reflects more blue.
(C) “Geometry of Au NP” - shape determines how/what directions oscillation can occur which affects what is absorbed/reflected
Different dimensions across different axis result in different absorption profiles for each axes - a combination of these leads to different absorption profiles
- Which of the following parameters does NOT dictate the absorption wavelength profile of gold nanoparticles (NP)?
(A) Separation distance between Au NP
(B) Size of Au NP
(C) Geometry of Au NP
(D) Amount of Au NP
(D) Amount of Au NP
Regarding:
(A) and (B) - same as Q4 on ‘Colour Emission’:
- (A) “Separation distance between Au NP” - can lead to multiple peaks or aggregation (causing different colour to be emitted) ← this can be used as a mechanism for biosensing (i.e. aggregation in the presence of a specific biomolecule)
- (B) “Size of Au NP” - larger NP → shift to larger wavelengths. As particles get larger, the absorption profile shifts towards the larger wavelengths (red-shift), and thus the solution reflects more blue.
(C) “Geometry of Au NP” - multidirectional oscillation in non-spherical NPs show multiple peaks (eg. rods have oscillation in both longitudinal and transverse directions → 2 peaks)
**Q4 and Q5 were basically same - the point of these two questions was to ensure the point that colour is in essence a function of wavelength absorption
- Which of the following statements regarding the relationship between colour and size of nanoparticles is correct?
(A) As particles get larger, the absorption profile shifts towards the larger wavelengths (red-shift), and thus the solution reflects more red.
(B) As particles get larger, the absorption profile shifts towards the larger wavelengths (red-shift) , and thus the solution reflects more blue.
(C) As particles get larger, the absorption profile shifts towards the shorter wavelengths (blue-shift), and thus the solution reflects more red.
(D) As particles get larger, the absorption profile shifts towards the larger wavelengths (blue-shift), and thus the solution reflects more blue.
(B) As particles get larger, the absorption profile shifts towards the larger wavelengths (red-shift) , and thus the solution reflects more blue.
- Red shift goes toward longer wavelengths, blue shift goes toward shorter wavelengths, but the colours look opposite because it’s absorbed, not reflected
- (i.e. more red shift means more red is absorbed → less reflected/looks more blue)
- Larger wavelengths “more red” (think infrared) shorter wavelengths “more blue” (think UV)
- Smaller gold NP = red, larger gold NP = blue/purple
- Which of the following statements best describes the processes and mechanisms involved in producing anisotropic Au NP of controlled shapes?
(A) Depending on the concentrations of the gold precursor, reductant and surfactant, the mixture spontaneously forms spherical seed NP of various sizes – this over time aggregate to form anisotropic Au NP of desired geometries.
(B) Control where the gold atoms are deposited on the seed Au NP; the shape of the resulting anisotropic Au NP depends on which crystallographic plane(s) the gold atoms bind to. The crystallographic plane on which the gold atoms bind to is controlled by adjusting the concentration and type of reagents in the solution used to synthesize anisotropic Au NP.
(C) Control where the gold atoms are deposited on the seed Au NP by controlling the temperature of the solution used to synthesize anisotropic Au NP; thermal energy in the system governs the movement (i.e. kinetics) of the Au atoms, and Au atoms bind at specific angles depending on the thermal energy in the system.
(D) The surfactants such as cetyltrimethylammonium bromide and other reagents within the synthesis solution act as a ‘template’ or ‘mould’ of nano-sized geometries, in which the gold atoms aggregate together to match the shape of the surrounding template.
(B) (1) Control where the gold atoms are deposited on the seed Au NP; (2) the shape of the resulting anisotropic Au NP depends on which crystallographic plane(s) the gold atoms bind to. The crystallographic plane on which the gold atoms bind to is controlled by adjusting the concentration and type of reagents in the solution used to synthesize anisotropic Au NP.
For example, certain surfactants preferentially bind to a particular plane - stops the gold atoms from binding to that plane, and forced to bind elsewhere → preferential direction(s) of growth → shape of nanoparticle
Regarding (D) - Incorrect:
“The surfactants such as cetyltrimethylammonium bromide and other reagents within the synthesis solution act as a ‘template’ or ‘mould’ of nano-sized geometries, in which the gold atoms aggregate together to match the shape of the surrounding template.” (<– kind of inspired from MSN production)
- Which of the following statements regarding aspect ratio of Au nanorods is FALSE?
(A) The optical properties of Au nanorods (e.g. wavelength absorption profile) is unaffected by changes in its aspect ratio.
(B) The optical properties of Au nanorods is a function of both its transverse and longitudinal surface plasmon resonance.
(C) Aspect ratio of Au nanorods can be controlled by controlling the molecular length of the surfactant used.
(D) Au nanorods are formed through the preferential binding of surfactants on certain crystallographic planes, forcing the gold atoms to bind to the seed towards a specified direction.
(A) The optical properties of Au nanorods (e.g. wavelength absorption profile) is unaffected by changes in its aspect ratio. - see the answers to Q4, 5, 6
Aspect ratio is a big part of optical properties or absorption profile (longitudinal absorption x transverse absorption i.e. option B)
- Which of the following molecules is generally used to covalently functionalize the surface of Au NP?
(A) Cetyltrimethylammonium bromide
(B) Sodium citrate
(C) Thiols
(D) Acetic acid
(C) Thiols (R-SH) using Au-S
Incorrect:
(A) Cetyltrimethylammonium bromide (surfactant that controls where the next atom binds, and also a surfactant to stabilize the nanoparticle
(B) Sodium citrate (stabilizer i.e. preventing unwanted aggregation)
(D) Acetic acid (used in controlling shape of NP)
- Negatively charged biomolecules such as small interfering RNA (siRNA) that could be delivered to alter gene expression can be conjugated onto Au NPs in which of the following approaches?
(A) Ionically, via charged surfaces
(B) Covalently, via corresponding nucleic acid strands
(C) Both (A) and (B)
(D) Neither (A) nor (B)
(C) Both (A) and (B):
(A) Ionically, via charged surfaces - (- i.e. negatively charged) siRNA strand attracted to (+ positively charged) surface of AuNP (modified surface, modified using charged molecules such as quartenary ammonium)
(B) Covalently, via corresponding nucleic acid strands - thiol on siRNA to bind to AuNP (i.e. Q9)
- Which of the following parameters of Au NP influence its endocytic uptake into mammalian cells?
(A) Shape of Au NP
(B) Size of Au NP
(C) Surface charge of Au NP
(D) All of the above
(D) All of the above:
(A) Shape of Au NP
(B) Size of Au NP - Certain combinations of shape/size of NP are better at being endocytosed/internalized → this affects photothermal therapy
(C) Surface charge of Au NP - positive charge favoured, neutral and negative charge NPs still internalised
- Which of the following statements regarding charged NP surfaces and their interaction with cells and biomolecules is FALSE?
(A) Proteins are more likely to denature on charged surfaces than neutral surfaces.
(B) Negatively charged nanoparticles cannot undergo endocytosis.
(C) Positively charged nanoparticles have higher affinity towards negatively charged cell membranes, compared to negative charged nanoparticles.
(D) Cells will endocytose positively charged nanoparticles in order to maintain the negative charge on the cell surface membrane.
- *(B) Negatively charged nanoparticles cannot undergo endocytosis.**
- False*, they can, it’s less likely/more work, but still possible (negatively charged nanoparticles have lower affinity to the positively charged cell membrane, but can still be internalized - matter of affinity)
True:
(A) Proteins (within which certain groups are also charged) are more likely to denature (i.e. change the configuration/shape of proteins) on charged surfaces than neutral surfaces.
- Define ‘photothermal therapy’ .
“Light-absorption by NP in vivo to produce heat in targeted cells”
NP + target injected → IR (700 - 2000nm range) shone at tissue → heat generated (depending of concentration, shape and size of NP)
More generally, therapy used where an electromagnetic wave source is applied onto an agent that generates heat as a result (anything that delivers this point would be marked 1)
→ gold NP is usually the best at this - because it has tunable absorption peak and a high photothermal conversions efficiency (Q15), and also it can interact with NIR (i.e. tunable absorption peak), and NIR can pass through tissue
- Name ONE clinical application of ‘photothermal therapy’.
- Primarily Cancer Therapy (suitable for patients not suited for radiotherapy, chemotherapy or surgical therapy) - using heat to kill off cancer cells where possible
- Imaging (thermal mapping, spatial temperature profiles etc.)
- Integration of biomaterial with tissue (e.g. cardiac patch i.e. heating the border of the patch to ‘stick’ the patch onto the heart without sutures)
- Name ONE physical property requirement for the nanoparticle to be used for
‘photothermal therapy’ (aside from size).
- Tunable absorption peak
- high photothermal conversion efficiency
- Shape of NP ← not a requirement per se; shape does influence photothermal effect (temperature wise)
- what if shape determines if it gets internalised? ← shape definitely does determine the ‘internalization efficiency’, but again, it’s not a specific requirement for photothermal therapy (i.e. compare this with other nanoparticles, e.g. MSN - you can control the shape of these NP for better internalization, but doesn’t mean that these can undergo photothermal therapy)
