Description:Field of invention
[001] The present invention relates to A system and method for metal ions
detection using carbon quantum dots (CQDs) biosensor. More particularly, it
deals with the preparartion of Carbon quantum dots (CQDs) with castor leaves
as precursor. CQDs presents a novel category of nanocarbon substances which
have attracted significant attention recently. CQDs are used in various fields such
as chemical sensing, biosensing, nanomedicine, solar cell technology, lightemitting diodes (LEDs), and electrocatalysis. CQDs exhibit exceptional physical
and chemical attributes, including high crystallinity, excellent dispersibility, and
notable photostability. Owing to their small size, and rapid electron transfer,
CQDs enhance the electrical conductivity and catalytic activity of composite
materials in which they are incorporated. Additionally, the rich abundance of
functional groups on the surface of CQDs simplifies the creation of multicomponent catalysts with enhanced electrical activity. More particularly, it deals
with the preparation of Carbon quantum dots (CQDs) via hydrothermal
carbonization, using castor (Ricinus communis) leaves as a natural precursor. The
used technique is a one-step, economical, and environmentally friendly method
for CQDs preparation. The prepared CQDs were further characterized by highresolution transmission electron microscopy (HR-TEM), X-ray photoelectron
spectroscopy (XPS), Energy-dispersive X-ray spectroscopy (EDX), and
Photoluminescence (PL) spectroscopic techniques to investigate their size, shape,
elemental composition, and optical characteristics.
3
Background and prior art
[002] Biosensors are being increasingly recognized by the scientific and medical
community as being implicated in many infections, and especially their
contribution to the recalcitrance of infection treatment. Biofilms are etiologic
agents for a number of disease states in mammals and are involved in 80% of
infections in humans. Examples include skin and wound infections, middle-ear
infections, gastrointestinal tract infections. The hitherto known prior arts
extensively talks about diverse synthesis methods for various layered double
hydroxides employed for various applications. Many prior art documents are
cited here. However, none of them discloses any attempt to synthesize CQD from
castor leaves precursor.
1. H. Huang et al., “One-pot green synthesis of nitrogen-doped carbon
nanoparticles as fluorescent probes for mercury ions,” RSC Adv, vol. 3, no. 44,
pp. 21691–21696, 2013, doi: 10.1039/c3ra43452d.
2. T. S. and R. S. D., “Green synthesis of highly fluorescent carbon quantum dots
from sugarcane bagasse pulp,” Appl Surf Sci, vol. 390, pp. 435–443, Dec. 2016,
doi: 10.1016/j.apsusc.2016.08.106.
3. D. Bano, V. Kumar, V. K. Singh, and S. H. Hasan, “Green synthesis of
fluorescent carbon quantum dots for the detection of mercury(ii) and glutathione,”
New Journal of Chemistry, vol. 42, no. 8, pp. 5814–5821, 2018, doi:
10.1039/c8nj00432c.
4
4. F. P. Pandey, A. Rastogi, and S. Singh, “Optical properties and zeta potential
of carbon quantum dots (CQDs) dispersed nematic liquid crystal 4'- heptyl-4-
biphenylcarbonitrile (7CB),” Opt Mater (Amst), vol. 105, p. 109849, Jul. 2020,
doi: 10.1016/j.optmat.2020.109849.
5. J. Zhou, Z. Sheng, H. Han, M. Zou, and C. Li, “Facile synthesis of fluorescent
carbon dots using watermelon peel as a carbon source,” Mater Lett, vol. 66, no.
1, pp. 222–224, Jan. 2012, doi: 10.1016/j.matlet.2011.08.081.
6. S. Patra et al., “One-step green synthesis of in–situ functionalized carbon
quantum dots from Tagetes patula flowers: Applications as a fluorescent probe
for detecting Fe3+ ions and as an antifungal agent,” J Photochem Photobiol A
Chem, vol. 442, p. 114779, Aug. 2023, doi:10.1016/j.jphotochem.2023.114779.
7. US9642919B2:
This invention relates to layered double hydroxide (LDH) materials and in
particular to new methods of preparing improved LDH materials which have
intercalated active anionic compounds (improved LDH-active anion materials).
The improved LDH-active anion materials are characterized by their high degree
of robustness, demonstrated by their high Particle Robustness Factor values, and
by their ability to retain substantially all of the intercalated active anionic
compound, in the absence of ion exchange conditions and/or at pH>4.
Detailed Description
[003] The object of the invention is to provide A system and method for metal
ions detection using carbon quantum dots (CQDs) biosensor precursor
comprising high-resolution transmission electron microscope (HRTEM) for
imaging crystallographic structure of the sample, XPS recorder to record
spectrum of the precursor sample, X-rays source, FTIR spectrometer,
photoluminescence analyzer, light source, waterbath, autoclave and syringe fitter
wherein the method comprising following steps;
5
a. drying castor leaves at temperature 800C for 24 hrs to get a dry sample
b. grinding the dry sample to make a fine powder
c. mixing 0.25gm of dry power in 40ml of de-ionized water to prepare a precursor
sample
d. ultrasonicating the above prepared sampe for 1 hr
e. filtering the said mixture into a 50ml teflon-lined hydrothermal autoclave and
reacting the contents for 3 hrs at 2000C and allow the autoclave to cool naturally
f. filtering the cooled mixture through syringe fitter to obtain the carbon quantum
dots(CQDs)
g. CQDs prepared by the above method steps are kept at temperature about 40C
and dark place for using metal ion detection.
The obtained results suggest that CQDs are nearly spherical, uniformly
distributed, have non-uniform sizes (1.5-4.5 nm) with an average of 2.7 nm,
and are weakly crystalline. with the importance of CQDs in today's society
stems from its ability to provide technical solutions to a variety of energy,
environmental and health concerns. CQDs are basically nano particles of
carbon having sizes in the range of nanometre, usually less than 10 nm.
CQDs have several advantages, including a low degree of toxicity,
ecological sustainability, affordability, straightforward synthesis, and
excellent resistance to photobleaching. CQDs are also recognised for their
strong and adjustable fluorescence, which can be controlled by their size,
surface modification, and doping levels.
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[004] Due to these exceptional properties, they have substituted
conventional dyes and semiconductor quantum dots in many applications
including biosensors, photocatalysts, optoelectronic devices, etc. CQDs are
still a very new and evolving field of study, with numerous obstacles and
prospects for additional investigation and invention.
[005] There preparation methods include top-down and bottom-up
approaches. The top-down strategy entails breaking down big carbon
materials into smaller CQDs using physical or chemical methods such as
laser ablation, arc discharge, chemical oxidation, or ultrasonication. The
bottom-up strategy involves constructing CQDs from smaller organic
molecules using chemical reactions such as polymerization, carbonisation,
solvothermal, or hydrothermal synthesis.
[006] Furthermore, many natural precursors like, lemon juice, fish scale, red
lentils, glucose, orange juice, tea leaves, soya milk, Honey, coffee grounds,
Aloe Vera, garlic peel, sugarcane juice, watermelon juice, cow milk, konjac
flour grass, sweet pepper, rose heart radish, hair etc. were used in the past.
In comparison to synthetic materials, natural precursors are more abundant,
renewable, and biodegradable. They also offer rich and varied carbon
sources, improving the biocompatibility and biosafety of CQDs. So, despite
of many utilized precursor in the past search for new ones continued.
[007] We have utilized a brand-new natural precursor in the form of castor
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leaves for CQDs synthesis. To the best of our knowledge castor leaves has
not been used in the past for CQDs preparation. Because heavy metal ions
are extremely poisonous, non-degradable, and can build up in living things,
producing a variety of health issues as well as environmental damage, it is
crucial to detect them. Consequently, it's critical to keep an eye on the
concentrations of heavy metal ions in food, soil, and water as well as to
eliminate them from the environment using efficient techniques.
Fluorescent probes based on fluorescence quenching mechanism are best
choice for these metal ion detection as they are fast, simple selective, and
sensitive.
[008] In one of the embodiments, the CQDs are prepared by hydrothermal
technique using castor leaves for the first time as a natural precursor. The
prepared CQDs has excellent optical properties and photostability. Due to
the presence of various functional groups on their surface they are found
selective and sensitive to Fe3+ ions.
[009] They are mainly composed of carbon (82.64 %), nitrogen (1.33 %),
and oxygen (16.02 %) and comprise various carbon, nitrogen, and oxygencontaining functional groups including carbonyl, hydroxyl, etc. They have
broad excitation and emission bands in UV and visible region respectively.
They possess excellent photostability in UV, fluorescent light, and salty
conditions.
8
They were found selective and sensitive to Fe3+ ions in an aqueous medium
based on which they were utilized for Fe3+ ions detection with the lowest
limit of detection (LOD) of 19 µM.
Sample Preparation
[010] Castor (Ricinus communis) leaves were obtained from the campus of
the National Institute of Technology Hamirpur, in India. stannous chloride
(SnCl2.2H2O, >98%), nickel chloride (NiCl2.6H2O, >98%), lithium chloride
(LiCl, >99%), potassium chloride (KCl, >99%), magnesium nitrate
(Mg(NO3)2.6H2O, >98%), calcium chloride (CaCl2.2H2O, >98%), cadmium
chloride (CdCl2.H2O, >99%), manganese chloride (MnCl2.4H2O, >98%),
aluminum nitrate (Al(NO3)3.9H2O, >98%), quinine sulfate
((C20H24N2O2)2.H2SO4.2H2O, >99%), mercuric chloride (HgCl2, >98%),
zinc chloride (ZnCl2, >98%), lead nitrate (Pb(NO3)2, >99%), titanium
dioxide (TiO2, >98%), iron chloride (FeCl3, >98%), hydrochloric acid (HCl),
sodium chloride (NaCl), sodium hydroxide (NaOH), and Deionized water
(DI) are used to prerpare the said precursor.
[011] The HR-TEM study was performed on the F.E.I. company of the
U.S.A. instrument (Model: FP5022/22-Tecnai G2 20 S-TWIN). XPS was
recorded on Thermofisher Scientific (Model: Nexsa base) with Al Ka Xrays. FTIR analysis was carried out on a Perkin-Elmer spectrum (65)
spectrometer. UV-visible spectra were obtained using a PerkinElmer UV2450 spectrophotometer.
9
Photoluminescence properties were analyzed using Shimadzu's RF-6000
Spectro fluorophotometer instrument (equipped with a Xenon lamp). A 365
nm UV lamp and an 8-watt fluorescent bulb were used to perform
Photostability tests. A water bath connected with a Spectro
fluorophotometer was used to maintain the temperature of the sample.
[012] CQDs synthesis
Castor leaves taken from the plant were dried at 80 °C for 24 hours and were
ground to a fine powder. 0.25 gm fine powder was mixed with 40 ml of
deionized water and ultrasonicated for 1 hour. It is now filtered to remove
the unmixed powder. The obtained mixture solution is then transferred to a
50 ml teflon-lined hydrothermal autoclave reactor. The reaction time is 3
hours at 200 °C. The reactor is then allowed to cool naturally. CQDs were
filtered with a 0.22 µM syringe filter and stored in cool (4 °C) and dark
conditions for further use.
[013] Photostability measurements The photostability of CQDs was
analyzed under four conditions: UV irradiation, fluorescent lamp, pH levels, and
high salt. In the UV irradiation and fluorescent light experiment, a diluted
solution of CQDs was exposed to UV (258 nm) and fluorescent light for 140
minutes, with PL intensity measured every 20 minutes. Sodium hydroxide
(NaOH) and hydrochloric acid (HCl) were used to prepare solutions of different
pH values. For high salt conditions, various concentrations of Sodium chloride
(NaCl) ranging from 0-1 M in deionized water were prepared. All the tests were
carried out at room temperature and PL intensity was monitored at 381 nm
excitation wavelength.
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[014] Fluorescent sensing of Fe3+ ions
The stock solutions of different metal ions (concentration 2 mM) were prepared
in deionized water. For the selectivity test, 2 ml diluted CQDs and 100 µL metal
ion solution were mixed and left for 2 minutes, followed by recording the PL
intensity at 381 nm excitation wavelength. The sensitivity of CQDs toward Fe3+
ions was investigated in various concentrations (0-300 µM) of Fe3+ in deionized
water. Fe3+ ions sensing in mixed metal ions was carried out by adding CQDs in
Fe3+ and other metal ions solution.
[015] Detection limit (LOD) calculations
The lowest limit of detection value is calculated using the following equation:
?????? = 3
??
??
Where LOD is the detection limit, s and s are the standard error of intercept and
slope of the graph between normalized PL intensity vs Fe3+ ions concentrations.
Description with respect to Drawings
[016] Figure 1 shows the size estimation, shape, and crystallinity of CQDs were
determined by using HR-TEM. Black circular spots as depicted in Figure 1 (a)
may indicate the formation of CQDs. The Inset of Figure 1(a) is the HR-TEM
image of CQDs at 500 pm resolutions. The presence of discrete lattice fringes in
the HR-TEM study of CQDs gives solid evidence of their crystalline structure.
The presence of these lattice fringes indicates an organized atomic arrangement
within the CQDs, implying a high degree of crystallinity. They are nearly
spherical, and uniformly distributed with an average diameter of 2.7 nm. The size
of CQDs was estimated from HR-TEM analysis using ImageJ software and the
results are shown in Figure 1 (b).
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As observed from the figure they have non-uniform sizes ranging from 1 to 5 nm
with an average of 2.7 nm. Hence, HR-TEM analysis suggests that CQDs are
nearly spherical, have a crystalline nature, non-uniform size distribution with an
average of 2.7 nm.
[017] Figure 2 shows elemental composition XPS analysis was used to
understand the Elemental composition and surface chemistry of CQDs. Three
peaks with binding energies of 285.09 eV, 399.84 eV, and 532.15 eV were present
in the XPS spectra, as shown in Figure 2(a). These correspond to C1s, N1s, and
O1s, respectively. Furthermore, to know about the surface functional groups on
CQDs, the C1s, N1s, and O1s peaks are deconvoluted. C1s deconvolution XPS
spectra (Figure 2(b)) have three peaks at 284.7 eV, 286.2 eV, and 287.8 eV
corresponding to C-C, C-N, and C=O respectively. Two peaks located at 399.7
eV and 400.2 eV were attributed to N-H, N-C=O in N1s deconvolution spectra
(Figure 2(c)). O1s deconvolution spectra in Figure 2(d) indicate the presence of
C=O, C-OH, and O=C-O groups at binding energy 531.2 eV, 532.4 eV, and 533.3
eV respectively.
[018] Figure 3 shows Energy-dispersive X-ray spectroscopy (EDX), as shown in
Figure 3 (a) also supports the findings of XPS analysis. It also indicates the
presence of carbon, nitrogen, and oxygen in the CQDs with weight % of 82.64,
1.33, and 16.02 respectively. The zeta potential value for the CQDs is -24.2 mV
(Figure 3(b). This high negative value suggests, that CQDs have a high degree of
negative charge and electrostatic repulsion, and are more stable with less
tendency to agglomerate or flocculate.
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[019] Figure 4 presents the PL excitation and emission spectra. The excitation
band is from 250 nm to 450 nm i.e. in UV-Visible region with maximum
excitation wavelength of 381 nm. The emission spectra is recorded at 3812 nm
excitation wavelength and it ranges from 400 nm to 650 nm with maximum
emission at 471 nm. The emission is in the visible region of the spectra. They
show a broad excitation and emission band rather than characteristic excitation
and emission peaks. This is possible due to their non-uniform sizes and the
presence of multiple functional groups on their surfaces.
[020] Figure 5 shows the practical utility of CQDs, photostability is an important
parameter to consider. We have investigated the photostability of CQDs under
four conditions: UV irradiation, fluorescent lamp, pH levels, and high salt
conditions as depicted in Figure 5 (a-d). The details of the experimental
procedure are explained in the experimental section. In UV light, fluorescent light,
and high salt conditions no appreciable change in the PL intensity was observed,
suggesting that these factors do not influence the PL intensity and CQDs are
photostable with them. Furthermore, PL intensity changes when it is recorded at
different pH levels. It is minimal in highly acidic and basic pH environments, and
maximum is for neutral pH levels. It indicates that CQDs are suitable to work
within neutral pH regions. In summary, CQDs are found to be photostable in UV
irradiation, fluorescent lamps, high salt conditions, and suitable to work with in
neutral pH regions.
[021] Figure 6 presents the metal ions detection capability of CQDs was
examined based on their fluorescence quenching mechanism.
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Compared to other metal ions, CQDs are found selective and sensitive to Fe3+
ions. The selectivity of CQDs was tested in various metal ions including, Pb2+
,
Fe3+, Sn2+, Hg2+, Cd2+, Zn2+, Ca2+, Cu2+, Ti4+, Mn2+, Co2+, Mg2+, Na+
, Al3+, Ni2+
,
and Li+
. The procedure for the selectivity and sensitivity test is described in the
experimental section. They were shown to be sensitive to Fe
3+ ions because,
among other ions, only Fe3+ ions can significantly reduce PL intensity, as seen
in Figure 6 (a). Here, F and F0 are the PL intensity of CQDs with and without
metal ions respectively. Some other ions like Pb2+, Sn2+, Hg2+, Cu2+, Al3+, and
Ni2+ have also quenched the PL intensity, so to check whether, they interfere with
Fe3+ ion sensing, mixed metal ion sensing was performed, and obtained results
are shown in Figure 6 (d). it is clear from the figure that no appreciable change
in the PL intensity was observed after the addition of other metal ions with Fe3+
ions. Hence, it is concluded that other metal ions do not interfere with Fe3+ ion
sensing. Since CQDs are selective to Fe3+ ions, their sensitivity was also
investigated in the various concentrations of Fe3+ (Figure 6(b)). The PL intensity
decreases linearly with the increasing Fe3+ ions concentration. The normalized
PL intensity with Fe3+ ions concentrations is plotted in Figure 6(c). An excellent
linear relationship was observed in the range (0-300 µM). The lowest limit of
detection (LOD) value was calculated based on this linear graph region. The
calculation equation is explained in the experimental section. In our case, the
LOD value is 19.1 µM/L. This means that CQDs can detect as low as 19.1 µM
Fe3+ ions per litre of the aqueous solution.
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[022] A comparison of the similar CQDs-based metal ion sensors with their LOD
values is shown in Table 1.
Table 1. Comparison of CQDs-based metal ion detection sensors
Precursor Preparation
method
Size
(nm)
Detected
Metal
ions
Linear
range
(µM)
LOD
(µM)
Red lentils Hydrothermal 4 - 6 Fe3+ 2-20 0.10
Citric acid, urea,
and Tween® 80
Microwave 3.42 ±
0.71
Fe2+, Fe3+ 0-40 6.5,
2.5
Citric acid and
1-Aminopropyl3-
methylimidazoli
um.
Hydrothermal 2.5 -
4.5
Fe3+ 0-300 13.68
Diammonium
hydrogen citrate
and urea
Solid state
reaction
2 - 7 Fe3+ 25-300 19
Blueberry Hydrothermal - Fe3+ 12.5-100 9.97
Lignocellulosic
biomass
Hydrothermal 2-6 Fe3+ 15.6-62.5 0.91
Castor seeds Hydrothermal 1-24 Fe3+ 0-40 18
Alginic acid and
ethanediamin .
Hydrothermal 13.8 Fe3+ 0.0-0.05
mM
10.98
Diammonium
hydrogen citrate
and urea
Solid-state
reaction
2 -7 Fe3+ 0–300 19
Castor leaves Hydrothermal 1 – 4.5 Fe3+ 0-300 19.1
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[023] CNPs feature negatively charged functional groups on their surface,
making them potential electron donors. In comparison, Fe3+ is a 3d5
system with
partially filled d-orbitals. Because of their half-field nature, they typically absorb
electrons from CNPs surface negative surface groupings. Fe3+ has a considerable
affinity for CNPs, which causes fluorescence intensity quenching.
[024] Nearly spherical, non-uniform sized with an average of 2.7 nm, CQDs were
prepared using hydrothermal technique from castor leaves as a natural precursor
for the first time in this invention. They mostly contain carbon, nitrogen, oxygen
and various functional groups on their surfaces. They possessed excellent
photostability and excitation, emission in UV, Visible regions. They were utilized
as a fluorescent probe for Fe3+ metal ion detection. The lowest limit of detection
of the fluorescent probe is 19 µM. , Claims:We Claim;
1. A system and method for metal ions detection using carbon quantum dots
(CQDs) biosensor precursor comprising high-resolution transmission electron
microscope (HRTEM) for imaging crystallographic structure of the sample, XPS
recorder to record spectrum of the precursor sample, X-rays source, FTIR
spectrometer, photoluminescence analyzer, light source, waterbath, autoclave
and syringe fitter wherein the method comprising following steps;
a. drying castor leaves at temperature 800C for 24 hrs to get a dry sample
b. grinding the dry sample to make a fine powder
c. mixing 0.25gm of dry power in 40ml of de-ionized water to prepare a precursor
sample
d. ultrasonicating the above prepared sampe for 1 hr
e. filtering the said mixture into a 50ml teflon-lined hydrothermal autoclave and
reacting the contents for 3 hrs at 2000C and allow the autoclave to cool naturally
f. filtering the cooled mixture through syringe fitter to obtain the carbon quantum
dots(CQDs)
g. CQDs prepared by the above method steps are kept at temperature about 40C
and dark place for using metal ion detection.
2. The method of analyzing PL of CQDs as claimed in claim1 comprising;
a. preparing a diluted solution of CQDs,
b. exposing to UV radiation of wavelength of 258nm and flourescent light
for about 140 minutes,
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c. measuring PL intensity for every 20 minutes,
d. preparing a solution of varying PH values by mixing CQDs in Sodium
hydroxide and hydrochloric acid,
e. mixing NaCl in concentration ranges from 0-1M in deionized water at
room temperature,
f. analyzing and calculating the PL intensity at excitation wavelength of
381nm.
3. The method of detecting metal ions(Fe3+) using CQDs as claimed in claim1
comprising;
a. preparing a stock solution of different metal ions of concentration 0-300uM
by mixing in 2mM deionized water,
b. reacting 2ml quantity of diluted CQD with 100ul metal ion solution for about
2 minutes,
c. calculating the PL intensity at excitation wavelength of 381nm,
d. detecting Fe3+ ions by adding CQDs in Fe3+ ions and in different metal ions.
Dated: Applicant