Highly stable organic fluorescent nanorods for living cell ... · Highly stable organic fluorescent nanorods for living cell imaging Minhuan Lan1, †, Jinfeng Zhang1, †, Xiaoyue

Nano Res

1

Highly stable organic fluorescent nanorods for living

cell imaging

Minhuan Lan1, †, Jinfeng Zhang1, †, Xiaoyue Zhu1, Pengfei Wang2(), Xianfeng Chen1(), Chun-Sing

Lee1, and Wenjun Zhang1()

Nano Res., Just Accepted Manuscript • DOI 10.1007/s12274-015-0748-4

http://www.thenanoresearch.com on February 15, 2015

© Tsinghua University Press 2015

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Nano Research

DOI 10.1007/s12274-015-0748-4


cell imaging

Minhuan Lan1, †, Jinfeng Zhang1, †, Xiaoyue Zhu1, Pengfei

Wang2*, Xianfeng Chen1*, Chun-Sing Lee1, and Wenjun

Zhang1*

1 Center of Super-Diamond and Advanced Films

(COSDAF), Department of Physics and Materials Science,

City University of Hong Kong, Hong Kong SAR, P. R.

China.

2 Key Laboratory of Photochemical Conversion and

Optoelectronic Materials, Technical Institute of Physics

and Chemistry (TIPC), Chinese Academy of Sciences

(CAS), Beijing, 100190, P. R. China.

† These authors contributed equally.

Red fluorescent nanorods made of small organic molecules

possess large Stokes shift, high stability and low cytotoxicity

and can be applied for living cell imaging.

Provide the authors’ webside if possible.

Author 1, webside 1

Author 2, webside 2


cell imaging



†

Received: day month year

Revised: day month year

Accepted: day month year

(automatically inserted by

the publisher)

© Tsinghua University Press

and Springer-Verlag Berlin

Heidelberg 2014

KEYWORDS

Cell imaging, organic dye,

fluorescent nanorods,

DPP.

ABSTRACT

Metal-free, organic dye based fluorescent nanorods were prepared through a

simple solvent-exchange route. The as-prepared nanorods possess low toxicity

to living cells and excellent photostability, and are stable in solutions of various

pHs and high ionic strength and with the interference of metal ions. Compared

with the free DPP-Br molecules in THF, these nanorods exhibit larger Stokes

shift and broader absorption spectra and much improved photostability. With

all of these beneficial characteristics, we successfully demonstrated their

application as a good fluorescence probe for bio-imaging.

Nano Research

DOI (automatically inserted by the publisher)

Research Article

| www.editorialmanager.com/nare/default.asp

2 Nano Res.

1. Introduction

Accurate and timely detection of pathological

changes in human tissues provides a basis for early

disease diagnosis and successful treatment [1-3].

Among the emerging disease diagnosis methods,

biomedical imaging technique surpasses traditional

ones (e.g., biological fluids analysis and histological

section technique) in terms of having non-invasive

nature and low side effects and being able to quickly

and directly show the body's internal organizational

structure, shape, and organ function in a very

intuitive way [4, 5]. Therefore, considerable efforts

have been devoted to develop new imaging

approaches to enable precise reveal of pathological

changes. To date, various imaging techniques

including ultrasound imaging, X-ray computed

tomography imaging, nuclear magnetic resonance

imaging, nuclear medical imaging, infrared imaging

and microwave imaging have been developed and

some of them are already being applied in clinical

diagnosis [6-11]. Although effective, these methods

suffer from a number of disadvantages such as

complicated instruments, complex procedures, and

being time-consuming. Therefore, it is highly

desirable to seek further development of new

approaches for efficacious observation of

pathological changes from both scientific and

technical views.

Optical imaging of tissue offers potential

advantages in distinguishing different structures

according to their biological environment [12, 13].

Fluorescence (FL) imaging is one of a rapid emerging

technology which provides real-time in vitro and in

vivo functional imaging information with high

spatial resolution and image contrast, as compared

to many other existing optical imaging techniques

[14-16]. The key factor in fluorescence imaging

technique is the fluorescent material. Many organic

dyes have been demonstrated for cells and tissues

imaging [17, 18]. However, their current applications

are often limited by their poor photostability and

water dispersibility. Although alternative

semiconductor quantum dots are superior to organic

dyes in terms of these two aspects [19-22], the clinical

applications of these agents have been hindered due

to the high cytotoxicity [23-26]. In addition, the

stability and performance of organic dyes and

quantum dots are often affected by pH values and

transition metals ions [27, 28].

Overcoming these limitations would benefit many

advanced applications such as imaging in living cells

and other complex body fluids that contain various

ions or possess extreme pH values, and real-time

monitoring of dynamic biological process [29-31].

There have been various attempts to circumvent this

problem, such as the surface modification of

fluorophore with optimized ligands, and making

fluorescent molecules in the form of nanomaterials

[32, 33]. Among these approaches, organic dye based

nanomaterials combine the advantageous properties

of organic dye and quantum dots including

outstanding optical properties, low cytotoxicity, and

robust chemical inertness, and therefore are defined

as a new class of promising fluorescence materials

[34-36]. In addition, in contrast to semiconductor

quantum dots, the emission of organic dye based

nanomaterials mainly depends on their constituent

molecules. Therefore, they can be fabricated with

different shape and size with constant emission

wavelength. Due to these superior advantages of

organic dye based nanomaterials, various kinds of

nanoparticles (NPs) have been reported for cell

imaging and tumor targeting [37, 38], but it was

recently found that, comparing with spherical

particles, nanorods (NRs) feature a larger

surface/volume ratio which may be advantageous

since additional targeting ligands can aid in cell

binding, cellular uptake, and therapeutic

effectiveness [39, 40]. V. P. Chauhan et al. found that

the shape of nanomaterials is an important aspect in

the design of effective nanomedicines. NRs could

penetrate tumours more rapidly than nanospheres

due to improved transport through pores [41].

Another recent study also found that NRs, as

opposed to spherical NPs, appear to adhere more

effectively to the surface of endothelial of cells,

allowing for drug targeting and imaging to specific

types of cells [42].

Address correspondence to Wenjun Zhang, email: [email protected]; Xianfeng Chen, email: [email protected]; Pengfei Wang, email: [email protected].

www.theNanoResearch.com∣www.Springer.com/journal/12274 | Nano Research

3 Nano Res.

Scheme 1. The synthesis route of DPP-Br.

Inspired by these findings, we designed and

synthesised a rod-coil organic molecule

2,5-Bis(6-bromohexyl)-3,6-bis(4-bromophenyl)

pyrrolo [3,4-c] pyrrole-1,4(2H,5H)-dione (DPP-Br).

The advantage of DPP-Br is that it possesses large

and plane π-conjugated structure which can act as

the rod segment and two long hydrophobic chains

connecting to the N-positions which are used as the

coils. With such as structure, attractively, the DPP-Br

molecules can conveniently self-assemble into NRs

through hydrophobic interaction and strong π-π

stacking interaction. These as-prepared NRs exhibit

excellent photostability and strong resistance to

photobleaching, stable in various pH solutions and

at high ionic strength conditions. In addition, DPP-Br

NRs aqueous solution exhibit larger Stokes shift,

broader absorption spectra than the DPP-Br in THF

solution. More attractively, high concentrations of

heavy metal ions and amino acids do not affect the

fluorescence intensity of our NRs. Combining the

above superior properties with the low cytotoxicity

to living cells, DPP-Br NRs successfully acted as an

excellent fluorescence probe for living cell imaging.

2. Experimental

2.1 General Materials and Methods

Diisopropyl succinate, 4-bromobenzonitrile,

tert-amyl alcohol, potassium tert-butoxide, FeCl3,

1,6-dibromohexane, fluorescein disodium salt were

purchased from J&K Scientific Ltd. NaCl, KCl,

Mn(OAc)2-4H2O, Co(OAc)2, Ni(OAc)2,

Al(NO3)3-9H2O, Cu(OAc)2-H2O, FeCl3, Cs(OAc)2-H2O,

CeCl3-7H2O, LiNO3, Ba(OAc)2, MgCl2-6H2O, CdSO4,

HgCl2, PBS, RNA, DNA, cysteine (Cys),

homocysteine (Hcy), glutathione (GSH), serine (Ser),

valine (Val), tyrosine (Tyr), leucine (Leu), tryptophan

(Trp), alanine (Ala), aspartic acid (Asp), methionine

(Met), threonine (Thr), isoleucine (Ile), glycine (Gly),

argine (Arg), lysine (Lys), rhodamine B (RhB),

4',6-diamidino-2-phenylindole (DAPI),

(poly[2-methoxy-5-(2-ethylhexyloxy)-1,4-

phenylenevinylene] (MEH-PPV) and

3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium

bromide (MTT) were ordered from Sigma-Aldrich

Co. LLC. All chemicals were used as received

without further purification. Deionized water with a

conductivity of 18.2 MΩ cm-1 was purified through a

Millipore water purification system.

UV-vis absorption spectra were obtained on a

Perking Elmer Lambda 750 UV/vis/NIR spectrometer.

Fluorescence spectra were measured with a Horiba

Fluormax-4 spectrophotometer. 1H NMR (400 MHz)

and 13C NMR (100 MHz) spectra were collected on a

Bruker Advance-400 spectrometer with

tetramethylsilane as an internal standard.

Matrix-assisted laser desorption ionization-time of

flight (MALDI-TOF) mass spectra was obtained on a

Bruker Microflex mass spectrometer. Dynamic light

scattering (DLS) and Zeta-potential results were

recorded on Zetasizer 3000 HS (Malvern, UK).

Scanning electron microscopy (SEM) images were

taken with a FEI Quanta 200 FEG field emission

scanning electron microscope. All pH measurements

were made with a Eutech pH-meter PH 700. The

white light (400-800 nm) was generated from a xenon

light source (Solar-500).

2.2 Synthesis of DPP-Br

The synthetic route of DPP-Br is outlined in Scheme

1 with detailed procedures described below.

2.3 Synthesized compound 1

Under argon atmosphere, sodium (0.55 g, 24 mmol),

FeCl3 (0.025 g) and dry tert-amyl alcohol 14 mL) were

stirred and heated to 90 oC until complete dissolution.

The mixture was cooled to 50 oC and


4 Nano Res.

4-bromobenzonitrile (2.20 g, 12 mmol) was added

followed by reheating to 90 oC. A solution of succinic

acid dissopropyl ester (1.0 g, 4.8 mmol) in dry

tert-amyl alcohol (5 mL) was dropwisely added in 1

hour. After stirring for 24 hours, 10 mL of acetic acid

was added, and the mixture was heated to 120 oC

and maintained for 1 hour. Then the precipitate was

collected and repeatedly washed with hot water and

methanol, and dried under vacuum at 80 oC. Red

solid was obtained. (Compound 1, 1.55 g, yield:

70%).

2.4 Synthesized DPP-Br

0.9 g compound 1, potassium tert-butoxide (0.5 g)

and N-methyl-2-pyrrolidone (10 mL, NMP) were

mixed and heated to 60 oC. 1,6-dibromohexane (2 mL)

was slowly added and the mixture was stirred at 60 oC for 24 hours. After cooling to room temperature,

50 mL of toluene was added into the reaction

mixture and washed with water to remove the NMP.

The organic solution was concentrated and the crude

product was purified by column chromatography on

silica using dichloromethane as eluent to yield a red

powder. (DPP-Br, 0.6 g. yield: 39%). 1H NMR (CDCl3,

400Hz, ppm) δ 1.22-1.25 (2H), 1.31-1.37 (2H),

1.52-1.57 (2H), 1.74-1.78 (2H), 3.30-3.34 (2H), 3.70-3.74

(2H), 7.65 (8H). 13C NMR (CDCl3, 100Hz, ppm) δ

25.86, 27.30, 29.67, 32.46, 33.56, 41.67, 109.97, 125.95,

126.88, 130.05, 132.36, 147.39, 162.40. MALDI-TOF

Mass spectrum m/z: Calculated: 772; Found: 772.

Scheme 2. Preparation of DPP-Br nanorods.

2.5 Preparation of DPP-Br NRs

DPP-Br NRs were obtained by a co-precipitation

method according to Scheme 2. Two hundred

microliters of 1.5 mg/mL DPP-Br/THF solution was

dropped into 5 mL of aqueous solution by

microsyringe at room temperature under vigorous

stirring. During this process, the DPP-Br molecules

self-assemble into NRs through hydrophobic

interaction and strong π-π stacking interaction. After

stirring for 5 minutes, the THF in the solution was

removed by bubbling nitrogen at room temperature.

Finally, the NRs dispersion was obtained by

centrifugation for further spectra measurements.

2.6 Preparation of MEH-PPV NPs

MEH-PPV NPs were obtained by a co-precipitation

method similar with DPP-Br NRs. Two hundred

microliters of 1 mg/mL MEH-PPV/THF solution was

dropped into 10 mL of aqueous solution by

microsyringe over a period of 5 minutes under

vigorous stirring at room temperature. The THF in

the solution was removed by bubbling nitrogen at

room temperature.

2.7 Cell culture and in vitro imaging studies

A549 cells were obtained from Peking Union Medical

College and cultured in culture media (DMEM/F12

supplemented with 10% FBS, 50 unit/mL penicillin,

and 50 μg/mL of streptomycin) at 37 oC in a

humidified incubator containing 5% CO2. For cell

imaging studies, cells were seeded in a 6-well plate

at a density of 104 cells per well in culture media and

maintained at 37 oC in a 5% CO2/95% air incubator

for 24 hours. Then, the cells were incubated with 100

μL of DPP-Br NRs aqueous solution (20 μM) in

culture media for 4 hours at 37 oC. The cells were

stained with a blue fluorescence nuclei specific dye

DAPI before observation. The imaging was taken

using Nikon fluorescence microscopy.

2.8 MTT assay

A549 cells were seeded in a 96-well plate at a density

of 104 cells per well in culture media and maintained

at 37 oC in a 5% CO2/95% air incubator for 24 hours.

Then, the culture media were removed and the cells

were incubated in culture medium containing

as-prepared DPP-Br NRs or MEH-PPV NPs with


5 Nano Res.

different concentrations (0~13 μM) for 24 or 48 hours,

and washed with culture medium. An amount of 200

μL of fresh culture medium (without FBS) containing

MTT (20 μL, 5 mg/mL) was then added, followed by

incubating for 4 hours to allow the formation of

formazan crystals. Absorbance was measured at 570

nm. Cell viability values were determined according

to the following formulae: Cell viability (%) = the

absorbance of experimental group/the absorbance of

control group × 100%.

3. Results and Discussion

3.1 Morphology and photochemistry properties of

DPP-Br NRs

Fig. 1. (a) SEM image of the DPP-Br NRs. Normalized (b)

absorption and (c) FL spectra of DPP-Br in THF (black line) and

DPP-Br NRs in aqueous solution (red line), λex=470 nm. The

insets show the photograph and fluorescence pictures of free DPP-Br in THF (left) and DPP-Br NRs in water (right).

The effects of the synthetic parameters including the

dropping rate, concentration, temperature and the

stir speed on the morphology and size of DPP-Br

nanomaterials were firstly studied, as summarized in

Table S1 in the Electronic Supplementary Material

(ESM). The morphology and size of obtained DPP-Br

nanomaterials were characterized by SEM. As shown

in Fig. S1 in the ESM and Fig. 1a, small DPP-Br

organic molecules are self-assembled to stable

rod-like 1 D nanostructure (NRs) under the

preparing condition (a). DLS result shows that these

NRs have an average hydrodynamic diameter of

178.6 nm. The zeta-potential of such DPP-Br NRs in

aqueous solution is almost neutral (-0.3 mV).

However, in other preparing conditions, some 0 D

NPs could also been obtained. The UV-vis absorption

spectra of the DPP-Br NRs aqueous solution and

DPP-Br THF solution are presented in Fig. 1b. It can

be seen that free DPP-Br molecules in THF show an

absorption peak of 480 nm. In comparison, the

absorbance peak of DPP-Br NRs dispersed in water

exhibit a slight red-shift of around 10 nm.

Fluorescence emission spectroscopy reveals an

emission peak of free DPP-Br in THF at 539 nm

under 470 nm laser excitation, whereas the emission

spectrum of DPP-Br NRs in water red-shifts to 606

nm (Fig. 1c). The fluorescence quantum yield of the

DPP-Br NRs in water is approximately 3.5% by using

RhB as a reference system (the fluorescence quantum

yield of RhB in water is about 31%) [43]. The obvious

red-shift of the fluorescence spectra and decrease of

fluorescence quantum yield (55.6% in THF) may be

due to the strong intermolecular π-π interactions.

This similar phenomenon has also been observed in

other organic fluorescent nanomaterial prepared

from organic dyes with π-conjugated structures.

[44-46] The Stokes shift of the DPP-Br NRs is up to

116 nm, which is much larger than that of DPP-Br in

THF solution (only 69 nm). This is also particularly

larger than the typical Stokes shift of semiconductor

QDs. Such a large Stokes shift can efficiently

minimize self-absorption of the high energy part of

the NRs’ emission spectra and measurement

interference between excitation and scattered light.

These will result in improved signal-to-noise ratio in

bioimaging.

3.2 Fluorescence spectra recorded in different

conditions

Once we produced fluorescent DPP-Br NRs, we next

investigated their stability under different pHs and

the photostability upon light illumination. As

displayed in Fig. 2a, the fluorescence intensity of the

NRs is nearly the same in water and PBS. The

variation of pH from 2 to 13 does not have obvious

influence on the fluorescence of the NRs. This

demonstrates that the fluorescence intensity is

independent of pH in a wide range, which is

beneficial for their potential bio-imaging applications.

Photostability measurement indicates that the

absorbance of DPP-Br NRs retains over 80% of the

original intensity after being continuously irradiated

under a white light for 60 min while the absorbance

of DPP-Br in THF solution decreases 71%; and the

commercial organic dye (FITC) decreases 85% (Fig.

2b and Fig. S2 in the ESM) under the same

conditions. In line with the absorbance stability,

DPP-Br NRs aqueous solution exhibits much

stronger resistance to photo-bleaching than its THF

solution and FITC solution. After one hour

continuous illumination, the fluorescence of the NRs


6 Nano Res.

can retain 83% while DPP-Br in THF solution and the

FITC solution decrease 72% (Fig. 2c). In addition,

MEH-PPV NPs with an average diameter of 63 nm

(Fig. S3 in the ESM) were synthesized through

co-precipitation method and their photostability

were further investigated. As shown in Fig. 2b and 2c,

under white light irradiation, the absorbance and the

FL intensity of the NPs decreased to 5%. All above

results indicate that the as-prepared DPP-Br NRs

have excellent photostability. Moreover, the NRs

suspension can be stored for at least one week in air

at room temperature, without the observation of any

precipitates and with only slight loss of fluorescence

intensity (Fig. 2d).

Fig. 2. (a) The effect of pH value on the FL spectra of DPP-Br

NRs aqueous solution. A comparison of (b) photostability and (c)

photo-bleaching of DPP-Br NRs in aqueous solution, DPP-Br in

THF solution, the traditional fluorescein dye (fluorescein sodium,

FITC) and MEH-PPV NPs in aqueous solution. All samples were

continuously irradiated using a 500 W xenon lamp. The

absorbance and FL intensity were normalized. The corresponding

absorption and FL spectra after irradiation 0 to 60 min were

shown in Fig. S2 in the ESM. (d) Time-dependent normalized FL intensity of DPP-Br NRs aqueous solution at 606 nm.

The complexity of intracellular system presents a

great challenge to the living cell imaging. The FL

spectra of DPP-Br NRs were recorded in NaCl

solution with different concentrations to verify the

stability of DPP-Br NRs under high ionic strength

environments. As shown in Fig. 3a, only slight

increase of the FL intensities at 606 nm is observed

even in 1 M NaCl solution. This clearly reveals that

the DPP-Br NRs are stable at high ionic strength

conditions. In addition, heavy metal ions such as

Hg2+ and Cu2+ often quench the fluorescence of

semiconductor QDs and carbon NPs through redox

reactions or electron transfer [47, 48]. Thus, the metal

ions effect on the FL of DPP-Br NRs were carried out

by monitoring the FL intensity of the NRs aqueous

solution at 606 nm in the presence of metal ions that

may coexist in living cells. Remarkably, as shown in

Fig. 3b, trivial changes of the signal are observed

when the NRs are interfered with various types of

heavy metal ions (20 μM). Taking into account that

some biological molecules in biological systems may

affect the fluorescence property of fluorophores,

several typical amino acids, RNA and DNA were

added to the solution to examine the potential

influence. As shown in Fig. 3c, negligible variations

of the FL intensity of DPP-Br NRs aqueous solution

at 606 nm are observed with their exposure to a high

concentration of amino acids (20 μM), DNA or RNA

(0.1 mg/mL). Overall, all of these results indicate that

our DPP-Br NRs have great potential for bioimaging

applications under physiological conditions. It's

worth noting that our DPP-Br NRs show superior

photostability and comparable environment-stability

(pH, high ionic strength, metal ions and biological

molecules) to that of MEH-PPV NPs (a commonly

used organic fluorescent nanomaterial) (Fig. S4 in the

ESM).

Fig. 3. (a) The effect of NaCl concentrations (0, 0.025, 0.05, 0.1,

0.25, 0.5, 1.0 M) on the FL intensities of DPP-Br NRs aqueous

solution. Ic and I0 represent the FL intensity of the DPP-Br NRs

aqueous solution at 606 nm in the presence different

concentration and absence of NaCl, respectively. The effect of (b)

metal ions and (c) amino acids, RNA and DNA on the FL

intensity of DPP-Br NRs solution at 606 nm. IAnaylte and IBlank

represent the FL intensity of DPP-Br NRs aqueous solution at

606 nm in the presence and absence of kinds of anayltes. (d) Cell

viability values (%) estimated by MTT proliferation tests versus

incubation concentrations of DPP-Br NRs (0, 1.6, 3.2, 6.5, 13.0

μM) at 37 oC for 24 hours (black column) and 48 hours (red


7 Nano Res.

column).

3.3 Cytotoxicity and in vitro cell imaging

In order to assess the NRs for potential biomedical

imaging applications, the cytotoxicity of DPP-Br NRs

to A549 cells was investigated by the standard MTT

assay. The cell viabilities of A549 cells were examined

upon exposure to the DPP-Br NRs with different

concentrations. Fig. 3d shows that the NRs exhibit

low cytotoxicity. The viability of the cells after 24

hours incubation retains about 100% even at a

concentration of 13 μM. When the incubation

extends to 48 hours, the cell viability is still about

90%. This result is similar with MEH-PPV NPs (Fig.

S5 in the ESM).

After confirming that the DPP-Br NRs possess low

cytotoxicity and are stable in physiological

environments, we tested their practical application

for living cell imaging. A549 cells were again chosen

and the nuclei were stained with DAPI (blue

staining). The results are shown in Fig. 4, as expected,

a remarkable intra-cellular red fluorescence is

observed in Fig. 4c. The overlay of the NRs

fluorescence and nuclei staining in Fig. 4d suggests

that the NRs are predominantly delivered to the

cytoplasm of the cells.

Fig. 4. Subcellular localization of DPP-Br NRs monitored by

fluorescence imaging in A549 cells. (a) bright field channel; (b)

blue fluorescence channel (DAPI channel); (c) red fluorescence

channel (DPP-Br NRs channel); (d) Overlap of the above images. Scale bar is 40 μm.

4. Conclusions

In summary, heavy metal free, organic small

molecule based red fluorescence DPP-Br NRs were

prepared through a co-precipitation approach. The

as-prepared NRs are a promising candidate for

living cell imaging due to their combined

superiorities for bioapplications, including

outstanding fluorescence properties (large Stokes

shift, photostability, and high resistance to

photo-bleaching, good stability in wide pH range

and at high ionic strength condition), good water

solubility, and excellent biocompatibility.

Acknowledgements

This work was supported by General Research Fund

of Hong Kong (CityU 104911) and National Natural

Science Foundation of China (NSFC 51372213 and

NSFC 61176007).

Electronic Supplementary Material: Supplementary

material (The detailed preparing conditions of the

obtained nanomaterials and their corresponding

SEM images; photostability and anti-bleaching

measurements; environments stability and

cytotoxicity of MEH-PPV NPs) is available in the

online version of this article at

http://dx.doi.org/10.1007/s12274-***-****-*

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Nano Res.

Electronic Supplementary Material


cell imaging



†

Supporting information to DOI 10.1007/s12274-****-****-* (automatically inserted by the publisher)

Preparing

conditions

Concentration of

DPP-Br (mM)

Dropping rate

(second/drop)

Temperature

(oC)

Stir speed

(rpm)

a 2 2 25 1000

b 1 2 25 1000

c 0.5 2 25 1000

d 2 2 25 2000

e 2 2 25 500

f 2 5 25 1000

g 2 Quick injection 25 1000

h 2 2 50 1000

i 2 2 0 1000

Table S1. The detailed preparing conditions of the obtained nanomaterials.

Address correspondence to Wenjun Zhang, email: [email protected]; Xianfeng Chen, email: [email protected]; Pengfei Wang, email: [email protected].


Nano Res.

Fig. S1. (a~i) The SEM images of the obtained nanomaterials prepared using condition (a) to (i).

Fig. S2. (a~d) Absorption and (e~h) FL spectra of the DPP-Br NRs in aqueous (a, e), DPP-Br in THF (b, f), FITC

(c,g) and MEH-PPV NPs (d, h) in aqueous solutions after irradiation 0 to 60 min.


Nano Res.

Fig. S3. (a) SEM image of the MEH-PPV NPs. (b) The particle size distribution histograms of the NPs.

Fig. S4. (a) The effect of pH value on the FL spectra of MEH-PPV NPs aqueous solution (λex=500 nm). (b) The

effect of NaCl concentrations (0, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0 M) on the FL intensities of MEH-PPV NPs

aqueous solution. Ic and I0 represent the FL intensity of the MEH-PPV NPs aqueous solution at 568 nm in the

presence different concentration and absence of NaCl, respectively. The effect of (c) metal ions and (d) amino

acids, RNA and DNA on the FL intensity of MEH-PPV NPs solution at 568 nm. IAnaylte and IBlank represent the

FL intensity of MEH-PPV NPs aqueous solution at 568 nm in the presence and absence of kinds of anayltes.


Nano Res.

Fig. S5. Cell viability values (%) estimated by MTT proliferation tests versus incubation concentrations of

MEH-PPV NPs (0, 1.6, 3.2, 6.5, 13.0 μM) at 37 oC for 24 hours (black column) and 48 hours (red column).

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Highly stable organic fluorescent nanorods for living cell ... · Highly stable organic fluorescent nanorods for living cell imaging Minhuan Lan1, †, Jinfeng Zhang1, †, Xiaoyue