Encapsulation of Dual Emitting Giant Quantum Dots in Silica Nanoparticles for Optical Ratiometric Temperature Nanosensors
, Haiguang Zhao 3, Simona De Zio 1,†, Nicoletta Depalo 2,*, Federico Rosei 4, Alberto Vomiero 5,6, M. Lucia Curri 1,2 and Marinella Striccoli 2Round 1
Reviewer 1 Report
The manuscript entitled "Silica encapsulated dual emitting giant quantum dots 3 for optical ratiometric temperature nanosensors" by Fanizza et al. describes the preparation of a giant quantum dot core/shell system that employs a ratiometric method for temperature sensing. This is a very interesting and important topic particularly as temperature sesning with nanoscale precision is very important and particularly relevant in biological applications.
The manuscript is very well written and the results support the conclusions. I do have some comments that I would encourage the authors to address:
1) In figure 1, a histogram for the PSD should be included. Also, a TEM scale bar should be added to the image.
2) Was the temperature sensing done in biologically relevant media? Meaning, did the authors do this in PBS or other similar media?
3) What is the calculated thermal sensitivity at the various temperatures and what is the average value?
Finally, I recommend this manuscript for publication in Applied Sciences.
Author Response
Reviewer I
The manuscript entitled "Silica encapsulated dual emitting giant quantum dots 3 for optical ratiometric temperature nanosensors" by Fanizza et al. describes the preparation of a giant quantum dot core/shell system that employs a ratiometric method for temperature sensing. This is a very interesting and important topic particularly as temperature sensing with nanoscale precision is very important and particularly relevant in biological applications. The manuscript is very well written and the results support the conclusions. I do have some comments that I would encourage the authors to address:
1) In figure 1, a histogram for the PSD should be included. Also, a TEM scale bar should be added to the image.
As requested by the reviewer, size statistical analysis of the “giant” QD sample described in the Figure 1 has been added as inset in the TEM micrograph picture (Figure 1B) together with the TEM scale bar and the corresponding caption has been modified as follows:
Figure 1. Sketch of the giant PbS@CdS@CdS NCs (A) and TEM micrograph (B, scale bar 50 nm) with size statistical analysis (B, inset), UV-Vis absorption (C) and photoluminescence (D, λex= 400 nm, T= 294K) spectra of the core-shell-shell sample. The absorbance profile in the 540-600 nm wavelength range has been enlarged in the inset of panel C
2) Was the temperature sensing done in biologically relevant media? Meaning, did the authors do this in PBS or other similar media?
We thank the Reviewer for this comment. We have purposely chosen to perform temperature-dependent measurements of the amino functionalized silica coated “giant” QD sample in MilliQ water at pH= 6 since, at this stage of the functionalization, a pH slightly lower than neutrality ensures a good colloidal stability, as revealed by the positive and high ξ-potential measurement value, and, therefore, it allows spectroscopic measurements with limited scattering phenomena.
We have already proved, in our previous works, the stability of similar core-shell silica nanoparticles, based on different type of core QDs and surface functionalities in different media such as PBS, borate and biological media used for in vitro studies (see reference 30, 34, 41-43), demonstrating the relationship between silica surface chemistry and colloidal stability in each tested solvent-based dispersant.
In this regards, the purpose of this work is to provide a preliminary evaluation of the effectiveness of the silica encapsulation in retaining the temperature dependent optical response of the giant QDs by spectroscopic measurements, while further functionalization steps to engineering the silica/dispersant media interface will be performed for next in vitro application.
3) What is the calculated thermal sensitivity at the various temperatures and what is the average value?
We would like to thank the Reviewer for his/her comment. The thermal sensitivity here reported represents the slope of the curve that describes the optical response versus the temperature measured in Kelvin (K). Since, here, we found out a good linear dependence of the integrated PL intensity ratio on the temperature, a constant value of the sensitivity (0.01 K-1) in all the investigated temperature range (between 281 K and 333 K) is expected. In the revised version of the manuscript, we also added the average relative sensitivity, which represents the sensitivity calculated with respect to each integrated PL. As calculated from the experimental data, it increases from 0.19% K-1 to 0.2% K-1 moving from 281 K to 333K, and has an average value of about 0.2% K-1.
Reviewer 2 Report
The manuscript is clearly written and well organized. Successful silica-coating and the first attempt of functionalization of PbS@CdS@CdS GQD is encouraging. I wish authors a lot of success with next more "in vivo" measurements of their promising "nanothermometers". I found ms generally almost ready for its potential publication (for minor points and suggested rewriting, see, please, below) with the exception of figures and their legends, which should be improved for their better clarity:
Fig. 1 legend is not correct. Provide, please, description of panel A (indicate OLA, OA). Describe the inset of panel C and provide with y-axis numbers to clarify its magnification.
Revise, please, Fig.2.: I suggest to make a linear, certainly enlarged scheme of panel A as the top raw. Currently, it is impossible to grasp from it due to its small size and no description of individual steps in the legend. Make three TEM micrographs as the bottom raw of the image and crop images to be identically scaled, thus easier to be compared without need to refer to their different scale bars.
In D indicate by arrows the elongated nanostructures and state their yield in the figure legend! Rephrase the legend to be easier to follow.
Revise legend of Fig.4: Describe the inset scheme of panel A; remove (sketch panel A)…
Revise legend of Fig.5: Describe both panels…
Please rewrite 228-235. Currently it is very hard to follow. Partly applies for 200-202 too.
Minor points/suggestions (according to line numbers):
several places: when more items listed, use e.g./etc. or “and” before the last item
several places: hyphenate “complex” adjectives/adverbs (e.g. silica-encapsulated, dual-emitting, non-solvent), but I assume the language editing will help here (overall, used English great and easy to follow/read)
24 peculiar => rather “advanced” or so
48-50 provide citation
86 originates => produces or so
89 have been demostrated “to be"..?
91 toxicity of the heavy metal “ionts”; non-soluble heavy metals/elements cannot be toxic!
111 “carefully” out
129 state OA purity
132 5-polyoxyethylene
143 vigorously
155-6 5 mL; PbS@CdS
177 systems (43),
178 preliminary? prepared
193 PL…already written out?
199 rather “in” the biomedical field
220 remove “narrow” as your spectrum here is incomplete to surely state that
225 to “allow” their application
265 IGEPAL CO-520
283 drastically => effectively or so; I assume there is nothing drastic, rather an improvement:-)
288 investigated => rather hypothetized/speculated etc. as not experiments were done/shown here
294 ligand
295 ethanol…can, no comma
324 the higher percentage => please, quantify exactly!
328 TEOS volume":"
329-30 Incomplete sentences, please, rewrite
335 …investigated (48).
343 (pH 6). Next sentence fragmented.
345-358 merge in a single par?
352 selected => typical
366 remove “somehow”
384 more relevant => more apparent?
385 has been => can be
394 biological/biomedical temperature probes
Author Response
The manuscript is clearly written and well organized. Successful silica-coating and the first attempt of functionalization of PbS@CdS@CdS GQD is encouraging. I wish authors a lot of success with next more "in vivo" measurements of their promising "nanothermometers".
I found ms generally almost ready for its potential publication (for minor points and suggested rewriting, see, please, below) with the exception of figures and their legends, which should be improved for their better clarity:
Fig. 1 legend is not correct. Provide, please, description of panel A (indicate OLA, OA). Describe the inset of panel C and provide with y-axis numbers to clarify its magnification.
We are pleased that our work was overall well considered by the Reviewer. As requested by the reviewer Figure 1 has been changed by adding the description of the panel A, indicating the two type of ligands (oleic acid and oleyl amine) used as nanocrystals capping agent. Furthermore, the inset in panel C has been described in the caption and the y-axis number has been added.
Revise, please, Fig.2.: I suggest to make a linear, certainly enlarged scheme of panel A as the top raw. Currently, it is impossible to grasp from it due to its small size and no description of individual steps in the legend. Make three TEM micrographs as the bottom raw of the image and crop images to be identically scaled, thus easier to be compared without need to refer to their different scale bars.
In D indicate by arrows the elongated nanostructures and state their yield in the figure legend! Rephrase the legend to be easier to follow.
We thank the reviewer for the suggestion. We have changes Figure 4 in two raws, all scaled in order to have the same scale bar length for an easier comparison: the upper one with the synthetic scheme of the silica shell growth in water-in-oil microemulsion and the bottom raw with the three TEM images. An arrow symbol has been added to highlight the elongated structure. The caption has been rephrased as follows:
Figure 2. (A) Scheme of the water-in-oil microemulsion approach for silica shell growth: addition of the organic- capped giant QDs to the water-in-oil microemulsion (step 1), displacement of the native ligands at the QD surface by surfactant molecules and hydrolized TEOS (step 2), inclusion of the surface modified QDs inside the water pool of the inverse micelle (step 3) and formation of the siloxane network around the QDs (step 4). TEM micrographs (Scale bar 50 nm) of the silica nanostructures prepared using native GQDs (B) and oleyl amine-treated GQDs at increasing volume of GQDs: 30μL (C) and 80 μL (D). The reaction mixture consists of: 350 μL Igepal CO-520, 200 μL NH4OH, 50 μL TEOS and 30 μL APTS. The reaction is let to proceed overnight at 28°C temperature. Arrows are used in panel D to highlight the elongated multicore structures (32% yield)
Revise legend of Fig.4: Describe the inset scheme of panel A; remove (sketch panel A)…
Revise legend of Fig.5: Describe both panels…
Captions of Figure 4 and 5 have been rephrased as follows:
Figure 4. UV-Vis absorption (A) and fluorescence spectra in a 281-333 K temperature range (B, λex= 400 nm) of silica coated GQDs NPs. A sketch of the nanostructure is shown in panel A.
Figure 5. Figure 5 Scattered plot of and fitting line of (A) integrated PL of CdS (blue symbol and line, ICdS) and PbS (red symbol and line, IPbS) versus temperature and (B) ratiometric response (IPbS/ ICdS) versus temperature.
Please rewrite 228-235. Currently it is very hard to follow. Partly applies for 200-202 too.
The sentence from line 200-202 in the original version of the manuscript has been changed as follows in the revised version of the manuscript:
The interest towards such a GQDs system arises from their original fluorescent properties, that have been proved to provide an accurate read-out of the temperature with ultrahigh sensitivity [9] in a wide temperature range, thus being promising as fluorescent nanothermometry systems.
The sentence from line 228-235 in the original version of the manuscript has been changed as follows in the new version of the manuscript:
Direct ligand exchange [44], encapsulation in self assembled molecular structures [29, 30, 45], polymer coating [31] and silica shell coating [32-34] have been reported as possible strategy for the phase transfer of organic-capped NPs in water. Here, silica shell growth is used. The low toxicity and chemical stability of the silica structure, [46] that undergoes to dissolution only at acidic pH [47], and the easy integration of surface functional groups, needed for bioconjugation and site specific recognition reaction, make silica shell a suited biocompatible coating, able to limit any leakage in the surrounding environment of the heavy metals forming the GQDs.
Minor points/suggestions (according to line numbers):
several places: when more items listed, use e.g./etc. or “and” before the last item
several places: hyphenate “complex” adjectives/adverbs (e.g. silica-encapsulated, dual-emitting, non-solvent), but I assume the language editing will help here (overall, used English great and easy to follow/read)
24 peculiar => rather “advanced” or so
48-50 provide citation
86 originates => produces or so
89 have been demostrated “to be"..?
91 toxicity of the heavy metal “ionts”; non-soluble heavy metals/elements cannot be toxic!
111 “carefully” out
129 state OA purity
132 5-polyoxyethylene
143 vigorously
155-6 5 mL; PbS@CdS
177 systems (43),
178 preliminary? prepared
193 PL…already written out?
199 rather “in” the biomedical field
220 remove “narrow” as your spectrum here is incomplete to surely state that
225 to “allow” their application
265 IGEPAL CO-520
283 drastically => effectively or so; I assume there is nothing drastic, rather an improvement:-)
288 investigated => rather hypothetized/speculated etc. as not experiments were done/shown here
294 ligand
295 ethanol…can, no comma
324 the higher percentage => please, quantify exactly!
328 TEOS volume":"
329-30 Incomplete sentences, please, rewrite
335 …investigated (48).
343 (pH 6). Next sentence fragmented.
345-358 merge in a single par?
352 selected => typical
366 remove “somehow”
384 more relevant => more apparent?
385 has been => can be
394 biological/biomedical temperature probes
We thank the Reviewer for the careful reading of the paper. The revised version of the manuscript takes into account almost all the suggestions arisen by the Reviewer.
The title has been changed in “Encapsulation of dual emitting giant quantum dots in silica nanoparticles for optical ratiometric temperature nanosensors” to meet the Reviewer suggestion to use less complex adjectives/adverbs.
Reviewer 3 Report
In here the authors present a method to encapsulate a dual emission giant quantum dot within a silica shell. The encapsulation makes this material applicable for biological application.
All in all the work is well performed and presented. The only concern I have is the temperature sensing. Please add standard errors to the calibration curve and discuss the sensitivity with respect to published work using other optical temperature sensors.
Author Response
In here the authors present a method to encapsulate a dual emission giant quantum dot within a silica shell. The encapsulation makes this material applicable for biological application.
All in all the work is well performed and presented. The only concern I have is the temperature sensing. Please add standard errors to the calibration curve and discuss the sensitivity with respect to published work using other optical temperature sensors.
We thank the Reviewer for this comment. The error bar has been added to the calibration curves in in Figure 5.
Concerning the sensitivity, we would like to point out that our main goal in this study is to prove that the temperature sensitivity of giant QDs, already widely explored and accepted as colloidal nanothermometers (see reference 27, 9), is not affected by the growth of the silica shell. However, in order to take into account the comment arisen by the Reviewer, we added in the revised version of the manuscript the relative sensitivity value measured for different classes of ratiometric fluorescent materials, such as lanthanide based nanoparticles, carbon dots and other inorganic QDs structures for comparison. It is worth to note that their temperature response relies on mechanisms that are specific for each type of material, temperature range and environment; therefore, comparisons among diverse probes are effectively difficult. In addition, by taking into account each system advantages and limitations, the availability of diverse temperature probes at the nanoscale offers the possibility to select the system most suitable for the specific case of study.
