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Neurotransmitter Specific, Cellular-Resolution Functional Brain Mapping Using Receptor Coated Nanoparticles: Assessment of the Possibility.

Forati E, Sabouni A, Ray S, Head B, Schoen C, Sievenpiper D - PLoS ONE (2015)

Bottom Line: Gold nanoparticles (GNPs) with two different geometries (sphere and rod) and quantum dots (QDs) with different sizes were studied along with three different neurotransmitters: dopamine, gamma-Aminobutyric acid (GABA), and glycine.The absorption/emission spectra of GNPs and QDs before and after binding of neurotransmitters and their corresponding receptors are reported.The results using QDs and nanorods with diameter 25nm and aspect rations larger than three were promising for the development of the proposed functional brain mapping approach.

View Article: PubMed Central - PubMed

Affiliation: Electrical and Computer Engineering Department, University of California San Diego, La Jolla, CA 92098, United States of America.

ABSTRACT
Receptor coated resonant nanoparticles and quantum dots are proposed to provide a cellular-level resolution image of neural activities inside the brain. The functionalized nanoparticles and quantum dots in this approach will selectively bind to different neurotransmitters in the extra-synaptic regions of neurons. This allows us to detect neural activities in real time by monitoring the nanoparticles and quantum dots optically. Gold nanoparticles (GNPs) with two different geometries (sphere and rod) and quantum dots (QDs) with different sizes were studied along with three different neurotransmitters: dopamine, gamma-Aminobutyric acid (GABA), and glycine. The absorption/emission spectra of GNPs and QDs before and after binding of neurotransmitters and their corresponding receptors are reported. The results using QDs and nanorods with diameter 25nm and aspect rations larger than three were promising for the development of the proposed functional brain mapping approach.

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a) The standard results set for QSA-450 using Antigab as the receptor and Gab as the neurotransmitter.The pump wavelength was 300nm and the numbers in parenthesizes report the peak wavelength of each curve in units of nm.
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pone.0145852.g007: a) The standard results set for QSA-450 using Antigab as the receptor and Gab as the neurotransmitter.The pump wavelength was 300nm and the numbers in parenthesizes report the peak wavelength of each curve in units of nm.

Mentions: The absorption spectra of gold nanorods showed around 10nm redshift after binding to neurotransmitters. However, the peak in GNPs spectra is wide, due to the loss, which is not desirable in detecting the peak shift. In other words, the ratio of the peak shift (after binding to the analyte) to the peak width is a better measure of detection convenience in our approach. Therefore, nanoparticles with much higher resonance quality factor are preferred in this method. Alternatively, instead of GNPs, we can use QDs which typically have very narrow emission spectra. Quantum dots are two/multi level quantum systems which can emit photons with energies equal or greater than their bandgap, if pumped with high enough energy photons. The bandgap of a QD, as well as its excited and ground levels quantization, are mainly controlled by its size and material. However, particles in the vicinity of QD, along with the ambient medium, impose extra restrictions on the emitted spectrum, which is often explained via the Purcell effect [35]. In [36, 37], effects of plasmonic materials (GNPs and graphene) on the emission spectrum of a quantum dot are studied theoretically by forming and solving a quantum master equation [36, 38]. We studied two commercially available CdSSe/ZnS core/shell QDs from Ocean NanoTech [39] with emission peaks at 450nm (part no. QSA-450) and 540nm (part no. QSA-540). The full width of half maximum (FWHM) of the emission spectra of the studied QDs were 35nm. QDs were sourced from Ocean NanoTech, and were amine capped. 1:1 Molar ratio of active amine sites were activated with Thermo Fisher BS3 and then conjugated to the antibody. BS3 (Sulfo-DSS) is bis(sulfosuccinimidyl)suberate, an amine-to-amine crosslinker that is homobifunctional and water soluble. Excess 5:1 antibody was added and then purification was performed by dialysis. It was determined that extra amine groups were not readily purified when the QDs were received. Therefore, a pre-purification using dialysis was completed. all conjugations were performed at 25 C and pH 7.4 in PBS. QDs were pumped at 300nm wavelength and their emission spectra were measured using a florescence spectrophotometer. Fig 7 shows the standard results set for QSA-450 using Antigly as the receptor and Gly as the neurotransmitter. The emission peak of QSA-450 was shifted 6nm after binding to the neurotransmitter. The ratio of the peak shift to the FWHM for QSA-450 is 0.18, which is twice as the 0.09 ratio for NR6. This makes QD a definitely better choice than GNP to be used in our approach. Moreover, the excitation and emission wavelengths are different in QDs (the excitation is at a smaller wavelength, 300nm in our experiments) which makes emission detection much easier. This is a great advantage over GNPs whose scattering is at the same wavelength and much weaker than the excitation. Similar to GNPs, mixture of different QDs coated with different receptors can be used to discern neurotransmitters. Fig 8 includes the emission spectrum of the mixture of QSA-450 and QSA-540 with peaks at 451nm and 538nm. Then, QSA-450 and QSA-540 were coated with Antigly and Antidop, respectively. The emission spectra of the functionalized mixture before and after adding Gly and Dop are shown in Fig 8. The first peak in the spectrum of the functionalized mixture shifts 6nm post binding of Gly while the second peak remains almost at the same wavelength (with the tolerence of 1nm). Likewise, the second peak shifts 8nm post biding of Dop. This is exactly what we intended, as Dop(Gly) can only attach to and interact with QSA-540(QSA-450). Therefore, only the peak associated with QSA-540(QSA-450) changes in the mixture emission spectrum. Dop(Gly) cannot interact with QSA-540(QSA-450) because their distance is too large (since they are not brought together by receptors).


Neurotransmitter Specific, Cellular-Resolution Functional Brain Mapping Using Receptor Coated Nanoparticles: Assessment of the Possibility.

Forati E, Sabouni A, Ray S, Head B, Schoen C, Sievenpiper D - PLoS ONE (2015)

a) The standard results set for QSA-450 using Antigab as the receptor and Gab as the neurotransmitter.The pump wavelength was 300nm and the numbers in parenthesizes report the peak wavelength of each curve in units of nm.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4696845&req=5

pone.0145852.g007: a) The standard results set for QSA-450 using Antigab as the receptor and Gab as the neurotransmitter.The pump wavelength was 300nm and the numbers in parenthesizes report the peak wavelength of each curve in units of nm.
Mentions: The absorption spectra of gold nanorods showed around 10nm redshift after binding to neurotransmitters. However, the peak in GNPs spectra is wide, due to the loss, which is not desirable in detecting the peak shift. In other words, the ratio of the peak shift (after binding to the analyte) to the peak width is a better measure of detection convenience in our approach. Therefore, nanoparticles with much higher resonance quality factor are preferred in this method. Alternatively, instead of GNPs, we can use QDs which typically have very narrow emission spectra. Quantum dots are two/multi level quantum systems which can emit photons with energies equal or greater than their bandgap, if pumped with high enough energy photons. The bandgap of a QD, as well as its excited and ground levels quantization, are mainly controlled by its size and material. However, particles in the vicinity of QD, along with the ambient medium, impose extra restrictions on the emitted spectrum, which is often explained via the Purcell effect [35]. In [36, 37], effects of plasmonic materials (GNPs and graphene) on the emission spectrum of a quantum dot are studied theoretically by forming and solving a quantum master equation [36, 38]. We studied two commercially available CdSSe/ZnS core/shell QDs from Ocean NanoTech [39] with emission peaks at 450nm (part no. QSA-450) and 540nm (part no. QSA-540). The full width of half maximum (FWHM) of the emission spectra of the studied QDs were 35nm. QDs were sourced from Ocean NanoTech, and were amine capped. 1:1 Molar ratio of active amine sites were activated with Thermo Fisher BS3 and then conjugated to the antibody. BS3 (Sulfo-DSS) is bis(sulfosuccinimidyl)suberate, an amine-to-amine crosslinker that is homobifunctional and water soluble. Excess 5:1 antibody was added and then purification was performed by dialysis. It was determined that extra amine groups were not readily purified when the QDs were received. Therefore, a pre-purification using dialysis was completed. all conjugations were performed at 25 C and pH 7.4 in PBS. QDs were pumped at 300nm wavelength and their emission spectra were measured using a florescence spectrophotometer. Fig 7 shows the standard results set for QSA-450 using Antigly as the receptor and Gly as the neurotransmitter. The emission peak of QSA-450 was shifted 6nm after binding to the neurotransmitter. The ratio of the peak shift to the FWHM for QSA-450 is 0.18, which is twice as the 0.09 ratio for NR6. This makes QD a definitely better choice than GNP to be used in our approach. Moreover, the excitation and emission wavelengths are different in QDs (the excitation is at a smaller wavelength, 300nm in our experiments) which makes emission detection much easier. This is a great advantage over GNPs whose scattering is at the same wavelength and much weaker than the excitation. Similar to GNPs, mixture of different QDs coated with different receptors can be used to discern neurotransmitters. Fig 8 includes the emission spectrum of the mixture of QSA-450 and QSA-540 with peaks at 451nm and 538nm. Then, QSA-450 and QSA-540 were coated with Antigly and Antidop, respectively. The emission spectra of the functionalized mixture before and after adding Gly and Dop are shown in Fig 8. The first peak in the spectrum of the functionalized mixture shifts 6nm post binding of Gly while the second peak remains almost at the same wavelength (with the tolerence of 1nm). Likewise, the second peak shifts 8nm post biding of Dop. This is exactly what we intended, as Dop(Gly) can only attach to and interact with QSA-540(QSA-450). Therefore, only the peak associated with QSA-540(QSA-450) changes in the mixture emission spectrum. Dop(Gly) cannot interact with QSA-540(QSA-450) because their distance is too large (since they are not brought together by receptors).

Bottom Line: Gold nanoparticles (GNPs) with two different geometries (sphere and rod) and quantum dots (QDs) with different sizes were studied along with three different neurotransmitters: dopamine, gamma-Aminobutyric acid (GABA), and glycine.The absorption/emission spectra of GNPs and QDs before and after binding of neurotransmitters and their corresponding receptors are reported.The results using QDs and nanorods with diameter 25nm and aspect rations larger than three were promising for the development of the proposed functional brain mapping approach.

View Article: PubMed Central - PubMed

Affiliation: Electrical and Computer Engineering Department, University of California San Diego, La Jolla, CA 92098, United States of America.

ABSTRACT
Receptor coated resonant nanoparticles and quantum dots are proposed to provide a cellular-level resolution image of neural activities inside the brain. The functionalized nanoparticles and quantum dots in this approach will selectively bind to different neurotransmitters in the extra-synaptic regions of neurons. This allows us to detect neural activities in real time by monitoring the nanoparticles and quantum dots optically. Gold nanoparticles (GNPs) with two different geometries (sphere and rod) and quantum dots (QDs) with different sizes were studied along with three different neurotransmitters: dopamine, gamma-Aminobutyric acid (GABA), and glycine. The absorption/emission spectra of GNPs and QDs before and after binding of neurotransmitters and their corresponding receptors are reported. The results using QDs and nanorods with diameter 25nm and aspect rations larger than three were promising for the development of the proposed functional brain mapping approach.

Show MeSH
Related in: MedlinePlus