Synthesis and in vitro photobiological studies of porphyrin capped gold nanoparticles

Article abstract of DOI:10.1007/s12039-018-1539-8

Abstract: We describe the synthesis and characterization of a thiol-functionalized porphyrin derivative 2 and its gold nanoparticle conjugates. The porphyrin 2 exhibited its characteristic intense Soret absorption at 420?nm with a molar extinction coefficient value of 3.6×105M-1cm-1 and good fluorescence in the region of 650–660?nm. The porphyrin-capped gold nanoparticles (POPNPs) were synthesized from the citrate-capped gold nanoparticles by the ligand exchange method and characterized by spectroscopic and morphological analyses (UV–Vis, DLS and TEM). The broadening of the absorption spectrum and quenching of the fluorescence intensity for the porphyrin gold nanoconjugates suggest efficient incorporation of the porphyrin moiety onto the gold surface. The results of DLS and TEM analyses indicate that the nanoconjugate POPNPs are uniformly spherical in shape with a size of ca. 25±5nm and exhibits a negative zeta potential value of -16.0±2mV. The singlet oxygen generation efficiency of the porphyrin 2 and POPNPs was calculated and are found to be ca. 0.53 ± 0.02 and 0.43 ± 0.03 , respectively. The in vitro photobiological studies revealed that POPNPs exhibited enhanced photodynamic activity compared to their parent porphyrin derivative 2 with an IC ₅₀ value of 5μM in MDA MB 231 cell lines. The mechanism of the cell destruction was studied by Annexin-FITC and confirmed through TMRM assay. We observed the increase in the percentage of cell population corresponding to the late apoptotic stage ca. 37.7% and 51.2% for 5 and 10μM of POPNPs, respectively, thereby demonstrating their apoptotic-mediated cell destruction and use in PDT applications. Graphical Abstract: Synopsis We synthesized a thiol-functionalized porphyrin-based sensitizer 2 and its gold nanoparticles (POPNPs) and have investigated their photophysical properties, singlet oxygen generation and in vitro photobiological efficacy. Our results demonstrate that the incorporation of the sensitizer onto the surface of nanoparticles not only improved its solubility in the aqueous medium, photophysical and photobiological properties but also its potential as a novel sensitizer for photodynamic therapeutical applications. [Figure not available: see fulltext.].

Full text of DOI:10.1007/s12039-018-1539-8

J. Chem. Sci. (2018) 130:133
© Indian Academy of Sciences
https://doi.org/10.1007/s12039-018-1539-8
REGULAR ARTICLE
Special Issue on Photochemistry, Photophysics and Photobiology
Synthesis and in vitro photobiological studies of porphyrin capped
gold nanoparticles§
ALBISH K PAULa, DHANYA T JAYARAMa, P S SANEESH BABUb,
NAGAPPANPILLAI ADARSHa, SHAMEEL THURAKKALa,c, ASHA S NAIRb,∗ and
DANABOYINA RAMAIAHd,∗
aPhotosciences and Photonics Section, Chemical Sciences and Technology Division, CSIR-National Institute
for Interdisciplinary Science and Technology, Thiruvananthapuram 695 019, Kerala, India
bRajiv Gandhi Centre for Biotechnology, Thiruvananthapuram 695 014, Kerala, India
cAcademy of Scientific and Innovative Research (AcSIR), CSIR-NIIST Campus, Thiruvananthapuram 695 019,
Kerala, India
dCSIR-North East Institute of Science and Technology, Jorhat 785 006, Assam, India
E-mail: rama@neist.res.in; d.ramaiah@gmail.com; sasha@rgcb.res.in
MS received 26 May 2018; revised 13 July 2018; accepted 26 July 2018
Abstract. We describe the synthesis and characterization of a thiol-functionalized porphyrin derivative 2 and
its gold nanoparticle conjugates. The porphyrin 2 exhibited its characteristic intense Soret absorption at 420 nm
with a molar extinction coefficient value of 3.6 × 105 M−1 cm−1 and good fluorescence in the region of 650–
660 nm. The porphyrin-capped gold nanoparticles (POPNPs) were synthesized from the citrate-capped gold
nanoparticles by the ligand exchange method and characterized by spectroscopic and morphological analyses
(UV–Vis, DLS and TEM). The broadening of the absorption spectrum and quenching of the fluorescence
intensity for the porphyrin gold nanoconjugates suggest efficient incorporation of the porphyrin moiety onto
the gold surface. The results of DLS and TEM analyses indicate that the nanoconjugate POPNPs are uniformly
spherical in shape with a size of ca. 25 5 nm and exhibits a negative zeta potential value of − 16.0 2 mV.
The singlet oxygen generation efficiency of the porphyrin 2 and POPNPs was calculated and are found to be ca.
0.53 0.02 and 0.43 0.03, respectively. The in vitro photobiological studies revealed that POPNPs exhibited
enhanced photodynamic activity compared to their parent porphyrin derivative 2 with an IC50 value of 5 μM in
MDA MB 231 cell lines. The mechanism of the cell destruction was studied by Annexin-FITC and confirmed
through TMRM assay. We observed the increase in the percentage of cell population corresponding to the late
apoptotic stage ca. 37.7% and 51.2% for 5 and 10 μM of POPNPs, respectively, thereby demonstrating their
apoptotic-mediated cell destruction and use in PDT applications.
Keywords. Gold nanoparticles; porphyrin; MTT assay; singlet oxygen; apoptosis.
1. Introduction
efficient singlet oxygen generation, and negligible dark
toxicity are the essential characteristics for an ideal pho-
tosensitizer.4 Several chromophores were investigated
to study their photodynamic efficacies in different cell
lines.5–7 Among those chromophores, the porphyrin-
based molecules have been investigated extensively for
PDT applications. These systems exhibit intense red flu-
orescence with good quantum yields of triplet excited
state and singlet oxygen generation and excellent pho-
totoxicity, thereby making them suitable candidates as
photosensitizers for image guided therapy.8
Photodynamic therapy (PDT) serves as an effective
choice for the treatment of various cancers, which
involves the combination of light, oxygen and a photo-
sensitizing molecule.1–3 Strong absorption in the photo-
dynamic window (600–800 nm), where the tissue pen-
etration of light is maximum, high tumour specificity,
*
For correspondence
§
th
Dedicated to Professor M V George on the occasion of his 90
Birth Anniversary.
Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s12039-018-1539-8) contains
supplementary material, which is available to authorized users.
0123456789().: V,-vol

133 Page 2 of 9
J. Chem. Sci. (2018) 130:133
spectra were recorded on a PerkinElmer Model 882 infrared
1
spectrometer. H and 13C NMR spectra were recorded on
a 500 MHz Bruker Avance DPX spectrometer. Electronic
absorption spectra were recorded on a Shimadzu 2401 PC
UV–Vis–NIR spectrophotometer. Fluorescence spectra were
recorded on a PerkinElmer LS-55 spectrofluorimeter. Mass
spectra were recorded on a Thermo Scientific Exactive ESI-
MS spectrophotometer. Fluorescence lifetimes were mea-
sured using an IBH (FluoroCube) picosecond time-correlated
single photon counting (TCSPC) system. The samples were
excited with a pulsed diode laser at 440 nm (NanoLED-
11) with a repetition rate of 1 MHz. The detection system
consisted of a microchannel plate photomultiplier (5000U-
09B, Hamamatsu) with a 38.6 ps response time coupled
to a monochromator (5000M) and TCSPC electronics [data
station Hub including Hub-NL, NanoLED controller, and
preinstalled fluorescence measurement and analysis studio
(FMAS) software]. The fluorescence decay profiles were
deconvoluted using IBH data station software V2.1 and min-
χ2
Chart 1. Structure of thiol-functionalized porphyrin 2.
Gold nanoparticles are emerging as promising agents
for cancer therapy and are being investigated as drug car- imizing the
values of the fit to 1 0.1. Fluorescence
quantum yields were determined using tetraphenylporphyrin
(TPP)asthereferencecompound(Φs = 0.11intoluene).14,15
Fluorescence quantum yields of the samples, ΦF were calcu-
lated by Eq. 1,
riers, photothermal agents, contrast agents and radiosen-
sitizers.9 Nanoparticles may prevent the premature
release of photosensitizers and they also have the advan-
tage of enhanced permeability and retention for the
improved cellular uptake.8 Most of the applications and
studies of the functionalized nanoparticles involve the
core modification as well as changing the nature of the
stabilizing ligand. The core modification and change
in size would enable one to tune the electronic and
optical properties of the nanoparticles. However, the
ligand exchange reactions have been proven to be effec-
tive approach for the incorporation of functionality in
the ligands used in the thiol-capped nanoparticles and
are widely used to produce both polar and non-polar
nanoparticles.10–13
AsFun2
AuFsn2s
ΦF
=
u Φs
(1)
wherein, As and Au are the absorbance of standard and
unknown, respectively. Fs and Fu are the integrated areas of
fluorescence peaks of the standard and unknown and ns and nu
are the refractive indices of the solvents used for the standard
and unknown, respectively. Φs is the fluorescence quantum
yield of the reference.
2.2 Synthesis of 6-mercapto-hexan-1-ol
6-Bromohexanol (1 g, 5.60 mmol) was allowed to reflux with
thiourea (0.64 g, 8.40 mmol) and NaOH (0.1 M) in 1,4-
dioxane (4 mL) for 4 h. The reaction mixture was cooled
and the solvent was removed under vacuum. The pH of the
reaction mixture was adjusted to 4 by adding dilute. HCl and
the thiol derivative was extracted using dichloromethane. The
organic layer was dried over Na2SO4 and concentrated to give
6-mercaptohexanol as an yellow oil.
In this regard, we synthesized a thiol-functionalized
porphyrin 2 (Chart 1) and have incorporated this pho-
tosensitizer onto the citrate-capped gold nanoparticles.
Further, we have investigated the photobiological prop-
erties of the gold nanoparticles and found that the
porphyrin-incorporated gold nanoparticles are more
efficient in the cell destruction when compared to the
bare gold nanoparticles as well as the parent porphyrin
dye 2.
1
Yield: 0.563 g (75%); H NMR (500 MHz, DMSO-d6,
TMS): δ 3.65 (s, 1H), 3.5 (t, 2H, J = 2.4 Hz), 2.56 (t, 2H,
J = 2.3 Hz), 1.52–1.57 (m, 4H), 1.5 (s, 1H), 1.41–1.44 (m,
4H); 13C NMR (125 MHz, DMSO): δ 62.8, 34.5, 32.3, 28.2,
24.9, 24.6;ESI–MS:m/zCalcd. forC6H14OS:134.08, Found:
135.11 (M+ + 1).
2. Experimental
2.1 Materials and methods
2.3 Synthesis of the porphyrin 2
The chemicals and reagents used in the study were purchased
from SD Fine Chemicals, India; Sigma-Aldrich, USA; Merck Synthesis of porphyrin 2 involves the condensation of the
Chemicals, Germany and were used as such without fur- porphyrin 1, which was prepared as per the reported proce-
ther purification. All experiments were carried out at room dure16 with 6-mercaptohexan-1-ol in dry THF in
temperature (25 ◦C 1 ◦C), unless otherwise mentioned. IR presence of dicyclohexylcarbodiimide (DCC) and dimethyl

J. Chem. Sci. (2018) 130:133
Page 3 of 9 133
Scheme 1. Synthesis of the thiol-functionalized porphyrin derivative 2.
aminopyridine (DMAP). To an ice-cold solution of porphyrin starting materials as well as the products were
1 (2.26 g, 3.2 mmol) under argon atmosphere, DMAP (0.04 g,
0.32 mmol) was added and stirred for 15 min. To this,
DCC (0.72 g, 3.5 mmol) was added followed by the 6-
mercaptohexan-1-ol (0.43 g, 3.2 mmol) and stirred for 4 h.
The completion of the reaction was monitored by TLC. The
reaction mixture was filtered, concentrated and washed with
water and extracted using ethyl acetate. The organic layer
was collected, dried over Na2SO4 and purified using column
chromatography (5% methanol–chloroform mixture).
Yield: 1.76 g (67%); M.p. >300 ◦C; 1H NMR (500 MHz,
DMSO-d6, TMS): δ 10.05 (s, 3H), 8.93 (s, 6H), 8.80 (s,
2H), 8.35–8.28 (q, 2H), 8.06–8.04 (t, 6H), 7.96–7.94 (d, 2H,
J = 10), 7.26−7.24 (t, 6H), 4.45–4.40 (t, 1H), 2.02–2.00 (d,
2H), 1.49–1.44 (t, 2H), 1.34 (s, 4H), 1.31 (s, 4H), −2.85 (s,
2H); ESI–MS: m/z Calcd. for C51H42N4O5S: 822.97, Found:
822.28 (M+).
characterized by spectroscopic and analytical methods
such as IR, UV–Vis, NMR (Figure S1, Supplementary
Information) and high-resolution mass spectrometry
(HRMS).
3.2 Synthesis and characterization of porphyrin
capped gold nanoparticles (POPNPs)
The basic methodology for the synthesis of porphyrin
capped gold nanoparticles involved two steps: 1) prepa-
ration of the citrate-capped gold nanoparticles (AuNPs),
and 2) ligand exchange of citrate-capped gold nanopar-
ticles with the porphyrin derivative, 2. The synthesis of
citrate-capped gold nanoparticles involves the chemical
reduction of the gold precursor HAuCl4 (0.25 mmol/L)
by dissolved trisodium citrate (2.5 mmol/L) at 75 ◦C
from their aqueous solutions.17–23 The yellow col-
ored gold solution was turned into vine red, which
indicates the formation of AuNPs and confirmed by
the observation of the surface plasmon at 522 nm
through UV–Vis spectroscopy (Figure S2, Supple-
mentary Information). The ligand exchange between
3. Results and Discussion
3.1 Synthesis and characterization of the
thiol-functionalized porphyrin 2
Thethiol-functionalizedporphyrin2wassynthesizedby AuNPs and thiol porphyrin 2 was achieved by react-
the coupling reaction between previously synthesized ing AuNPs with the porphyrin derivative 2 in ethanol
carboxyl porphyrin derivative 1 and 6-mercaptohexan- (Scheme 2). The ligand exchange reactions were car-
1-ol using DCC and DMAP in THF as the solvent. ried out using different concentrations of the thiol
The latter was obtained from the 6-bromohexan-1-ol porphyrin, 2 (50 μM, 100 μM, 150 μM, 200 μM and
by treating with thiourea in dioxane (Scheme 1). The 250 μM) to optimize the particle stability. Out of these

133 Page 4 of 9
J. Chem. Sci. (2018) 130:133
Scheme 2. Schematic representation of the synthesis of the porphyrin-capped gold nanoparticles (POP-
NPs) from the citrate-capped gold nanoparticles.
A
B
420 nm
440 nm
655 nm
1.00
0.75
0.50
0.25
0.00
800
600
400
200
0
2
2
POPNPs
POPNPs
450
Wavelength, nm
600
600
700
Wavelength, nm
800
Figure 1. (A) Normalized absorption spectrum of the porphyrin 2 (1.4 μM) in methanol (black trace) and the
porphyrin-capped gold nanoparticles, POPNPs (red trace). (B) Fluorescence spectrum of the porphyrin 2 alone
(1.4 μM, black trace) and the POPNPs (red trace), excitation wavelength,
= 515 nm.
λ
ex
concentrations used, we obtained a maximum stability coefficient value of 3.6 × 105 M−1 cm−1 and quinoid
for the nanoparticles at a porphyrin concentration of bands at 515, 552, 589 and 645 nm in methanol, as
150 μM, which was evidenced through zeta potential shown in Figure 1a. The absorption spectrum of the
measurements(FigureS3, Supplementary Information). porphyrin-capped gold nanoparticles (POPNPs) was
The zeta potential value for the porphyrin bound gold found to be broadened due to the electronic interactions
nanoparticles (POPNPs) at 150 μM of porphyrin, 2 of the gold (surface plasmon of the gold nanoparticles)
was found to be −6.0 mV. Hence, we selected this with the porphyrin unit on the gold surface. Figure 1b
combination of gold nanoparticles for further studies. shows the fluorescence spectra of both the porphyrin
We observed a shift in the zeta potential value from and the porphyrin-capped gold nanoparticles. The flu-
− 40 2 mV to − 16 2 mV after the conjugation orescence of the porphyrin 2 at 655 nm was quenched
of the porphyrins onto the gold nanoparticles, which completely after ligand exchange with citrate capped
points towards the successful ligand exchange reaction AuNPs indicating the effective incorporation of the por-
and the citrate has been partially replaced by the por- phyrin moiety onto the gold surface. The fluorescence
phyrin.
quantum yield of the porphyrin 2 was determined to be
The thiol-functionalized porphyrin 2, showed the ca. 0.08 0.002 using tetraphenylporphyrin (TPP) as
characteristic absorption and emission profiles of the the standard,14 whereas for the POPNPs, the value was
porphyrin chromophore. It showed a Soret band in the found to be negligible. To have a better understanding of
absorption spectrum around 420 nm with extinction the fluorescence changes observed for the porphyrin as

J. Chem. Sci. (2018) 130:133
Page 5 of 9 133
A
B
10000
8000
6000
4000
2000
10000
1274 nm
Hp
2
POPNPs
2
1000
100
10
POPNPs
1
0 10 20 30 40 50 60 70 80 90 100
Time, nS
1150
1200
1250
1300
1350
1400
Wavelength, nm
Figure 2. (A) Fluorescence decay profiles of the porphyrin 2 (green trace) and POPNPs (red trace). (B)
Singlet oxygen luminescence at 1274 nm of Hematoporphyrin (Hp), porphyrin 2 and the nanoconjugate,
POPNPs in acetonitrile (OD adjusted to 0.25 at excitation wavelength, 530 nm).
Figure 3. TEM images of (A) bare AuNPs and (B) POPNPs.
well as in the nanoparticle surface, we have analyzed the good quantum yield values for POPNPs suggest that
emission decay of the porphyrin through time-resolved the developed nanosystem can be effectively utilized
fluorescence technique. The fluorescence decay profile for PDT applications.
of the porphyrin derivative 2 showed a monoexponen-
To understand the morphology of the synthesized
tial decay with a lifetime of ca. 8.9 ns. Notably, for gold nanoparticles, we carried out dynamic light scatter-
the POPNPs, the fluorescence lifetime was found to be ing (DLS) and transmission electron microscopy (TEM)
completely quenched (Figure 2a).
experiments.25–27 In DLS analysis, we observed the for-
The efficient generation of singlet oxygen is a mation of uniform spherical nanoparticles having a size
pre-requisite for a photosensitizing system to act as of ca. 29 5 nm in aqueous media for the citrate capped
a potential PDT agent. In this context, we examined nanoparticles (AuNPs) (Figure S4A, in Supplementary
the efficiency of the thiol porphyrin, 2 as well as the Information). In the case of POPNPs, we observed an
nanoconstruct POPNPs through the direct method of increase in the size of the particle with an average size
monitoring the singlet oxygen luminescence at 1274 nm of ca. 47 5 nm indicating that the ligand exchange was
by excitation at 530 nm (Figure 2b). The effective (Figure S4B, Supplementary Information). We
quantum yield of singlet oxygen generation for the have further carried out the morphological analysis of
porphyrin, 2 and the nanoconjugate, POPNPs were cal- the nanoparticles through TEM. TEM analysis of the
culated by using hematoporphyrin (Hp) as the standard citrate capped AuNPs (Figure 3a) confirmed that the
(ꢀꢁ = 0.61 0.02)24 and the values are found to be ca. nanoparticles were of spherical in shape with a size of
0.53 0.02 and 0.43 0.03, respectively. The observed ca. 20 nm. Figure 3b shows the corresponding TEM

133 Page 6 of 9
J. Chem. Sci. (2018) 130:133
Figure 4. (A) Histogram showing the % inhibition of porphyrin end-capped gold nanoparticles (POPNPs)
in MDA MB 231 cells in light and dark conditions. (B) Concentration dependent cytotoxicity of POPNPs
in dark and light conditions.
image of the POPNPs. Most of the particles were found microscopy and flow cytometry.28–30 To understand the
to be spherical in shape with an average size of ca. mechanism behind the PDT activity and cellular dam-
1
25 nm. Further, the H NMR spectrum of the POP- age induced by the porphyrin capped gold nanoparticles
NPs showed a peak broadening, which reveals that the (POPNPs), we investigated Annexin V-FITC/PI assay
thiol porphyrin is efficiently capped to the gold surface using flow cytometric analysis (Figure 5). The cell pop-
(Figure S5, Supplementary Information). In addition, ulations at different phases, namely, viable (Annexin
the IR spectrum of the POPNPs got broadened as com- V-FITC-/PI-), early apoptotic (Annexin V-FITC+/PI-)
pared to the thiol porphyrin 2 indicating the interaction and late apoptotic (Annexin V-FITC+/PI+) were exam-
of the porphyrin derivative 2 with the gold surface ined at different sensitizer doses. We observed that most
(Figure S6, in Supplementary Information).
of the cells were viable for the light control (by irradia-
tion in the absence of sensitizer) as well as for dark con-
trol (in presence of POPNPs (10 μM) in the absence of
light. The control irradiations were carried out by using
the porphyrin 2 alone as well as citrate-capped gold
nanoparticles alone and both of them showed negligible
toxicity, which indicates that porphyrin derivative 2 as
well as the gold nanoparticles are non-cytotoxic toward
MDA-MB-231 cells. Interestingly, upon illumination of
theporphyrin-cappedgoldnanoparticles(POPNPs), we
observed the cell death through both early and late apop-
tosis in a concentration depended manner. The percent-
age of cell population corresponds to the necrosis/late
apoptotic stage (Annexin V-FITC + /PI+) for 5 μM of
POPNPs was ca. 37.7% and 10 μM of POPNPs as ca.
51.2%, whereas in light control and in presence of 2
alone, we observed only ca. 0.2% and 1.7%, respec-
tively (Figure 5). These results clearly indicate that the
porphyrin-capped gold nanoparticles (POPNPs) induce
cell death through late stage apoptosis.
To confirm the apoptotic mediated cell destruction,
we have carried out tetramethylrhodaminemethyl ester
(TMRM) staining experiment. The changes in mito-
chondrial membrane potential via apoptosis were mon-
itored using the tetramethylrhodamine methyl ester
through fluorescence imaging. The decrease in the mito-
chondrial inner membrane potential due to apoptosis,
will results in the decrease in red fluorescence. We
observed that upon, photodynamic treatment of MDA-
MB-231 cells with POPNPs at 5 μM resulted in about
3.3 In vitro photobiological activity of
porphyrin-capped gold nanoparticles (POPNPs)
As the porphyrin derivative 2 and POPNPs were quite
efficient in generating singlet oxygen, we examined
their in vitro photobiological activity under different
conditions. To investigate the in vitro PDT of the POP-
NPs, we employed MTT assay in MDA MB 231 cell
lines (aggressive human breast cancer) using 70 W
Sodiumvaporlamp( > 590 nm), 100 J cm−2. Thehalf
λ
inhibitory concentration, IC50 value, was determined
for the porphyrin dye as well as the POPNPs at dark
and light conditions. The porphyrin derivative, 2 exhib-
ited photocytotoxicity with an IC50 value of 25 μM. In
contrast, we observed a significant enhancement in the
photocytotoxicity for the porphyrin capped nanoparti-
cles (POPNPs), which showed 5-fold better value of
IC50 of ca. 5 μM in MDA MB 231 cell lines (Figure 4).
The photocytotoxicity of citrate-capped gold nanopar-
ticles also evaluated as a control and which showed
negligible cytotoxicity.
In apoptotic cells, the membrane phospholipid
phosphatidylserine is translocated from the inner to
outer leaflet of the plasma membrane, thus exposing
phosphatidylserine to the external cellular environment.
Annexin V (tagged with FITC) has high affinity for
phosphatidylserine and therefore serves as a sensitive
probe for identifying apoptotic cells by fluorescence

J. Chem. Sci. (2018) 130:133
Page 7 of 9 133
Figure 5. Flow cytometric analysis of MDA MB 231 cells after PDT treatment with POPNPs; (A) light control, (B) presence
of 2 alone, (C) 5 μM of POPNPs, and (D) 10 μM of POPNPs.
Figure 6. TMRM assay for the estimation of mitochondrial membrane potential reduction: Quantification through FACS
analysis for (A) light control, (B) in presence of 2 alone, (C) 5 μM of POPNPs, (D) 10 μM of POPNPs.

133 Page 8 of 9
J. Chem. Sci. (2018) 130:133
ca. 34% decrease in membrane potential, whereas at
10 μM resulted in ca. 51.2% decrease in mitochondrial
membrane potential (Figure 6). On the other hand, the
light and dark controls showed only ca. 6% and 8%
decreases in mitochondrial membrane potential. These
observations confirm that the porphyrin-capped gold
nanoparticles induce cell death during PDT treatment
predominantly through apoptosis pathway.
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4. Conclusions
In conclusion, we synthesized and characterized a
thiol-functionalized porphyrin derivative 2 and inves-
tigated its photophysical as well as singlet oxygen gen-
eration properties. The good singlet oxygen generation
efficiency of the thiol porphyrin led us to the incorpora-
tion of this porphyrin derivative in the gold nanoparticle
surface by ligand exchange protocol. Various micro-
scopic and photophysical studies have revealed that the
thiol porphyrin was effectively incorporated into the
gold nanoparticle surface (POPNPs). Further, we have
carried out the cytotoxicity analysis of the gold nanopar-
ticles by employing MTT assay and found that the
porphyrin incorporated nanoparticles (POPNPs) were
cytotoxic only in presence of light with an excellent IC50
value of 5 μM. The mechanism of the photodynamic
action was found to be late apoptosis mediated cell
destruction as confirmed by FITC-Annexin and TMRM
assays. Our results demonstrate that porphyrin 2 can be
used as an efficient sensitizer for the stabilization of gold
nanoparticles thereby its effective use as a sensitizer in
photodynamic therapeutic applications.
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Supplementary Information for this article is available at
www.ias.a.in/chemsci.
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Joseph J and Ramaiah D 2016 Selective recognition
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