1

A quantum dot-based “off-on” fluorescent probe for biological

detection of zinc ions

Hu Xu, Zhiping Wang, Yan Li, Shijian Ma, Peiyi Hu, Xinhua Zhong*

Institute of Applied Chemistry, Department of Chemistry, East China University of Science and

Technology, Shanghai 200237, P. R. China

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2

Fig. S1 1H NMR spectra of DPA and DPA-DTC in [D6]DMSO.

(A)

(B)

e c

a

b

d

e c

a

b d

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3

3000 2000 1000

2873

2964

OAm

P-DTC

14281582

2855

Tra

nsm

itta

nce

Wavenumbers (cm-1)

2925

DPA-DTC

Fig. S2 The solid-state FTIR spectra of DPA-DTC, P-DTC, and OAm.

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4

Fig. S3 Wide-field TEM image of DPA-P-DTC-QDs. The insert shows the corresponding

HRTEM.

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5 6 7 8 910

15

20

25

30

PL

in

ten

sity

(a.u

.)

pH

Fig. S4 The PL intensity of DPA-P-DTC-QDs at different pH values in the absence of Zn2+

. (ex =

350 nm)

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6

0 10 20 30 40

2

4

6

8

10

10 nM

20 nM

30 nM

40 nMF

/F0

[Zn2+] (M)

Fig. S5 The effect of the concentration of DPA-P-DTC-QDs on PL enhancement of QDs for Zn2+

.

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7

0

2

4

6

8

10

Metal ions

Mixed ions

without Zn2+

Mixed ions

including Zn2+

F/F

0

Only Zn2+

Fig. S6 Relative PL response (F/F0) of DPA-P-DTC-QDs in the presence of (A) mixed ions

including Na+, K

+, Mg

2+, Ca

2+, Ba

2+, Co

2+, Ni

2+, Cd

2+, Mn

2+, and Pb

2+ ions (each at 0.125 mM)

except for Zn2+

, (B) mixed ions (each at 0.125 mM, no Cu2+

, Ag+, Fe

2+, Fe

3+, and Hg

2+ ions)

containing Zn2+

(16M), and (C) only Zn2+

(16M) at pH 7.5 (PBS, 10 mM).

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250 300 550 600 650

0

1

2

3

4

No

rma

lize

d I

nte

nsi

ty

Wavelength (nm)

Absorbance of DPA-DTC

Absorbance of P-DTC

QDs PL

Fig. S7 Normalized absorbance of DPA-DTC and P-DTC and normalized PL intensity of CdSe/ZnS

QDs.

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2.0 1.5 1.0 0.5 0.0 -0.5

0

20

40

60 Fc/Fc+

DPA-DTC

DPA-DTC+Zn2+

Cu

rren

t (

A, a

.u.)

E (V vs. SCE)

Fig. S8 Cyclic voltammograms of Fc/Fc+ (black curve), DPA-DTC in the absence of Zn

2+ (red

curve), and DPA-DTC in the presence of equimolar Zn2+

(blue curve) at scan rate 100 mV/s. For the

red and blue curves, except for the reversible peaks of Fc/Fc+ redox couple there is a very broad and

irreversible anodic peak in the range of 0.4–1.5 V, which can be assigned to the formation of

dithiocarbamate radicals via oxidation and the subsequent dimerization of these radicals to thiuram

disulfide (L. Marek, Zeszyty Naukowe Politechniki Gdanskiej, Chemia, 2003, 51, 3–96.). This

transformation should always exist in DPA-DTC containing system whether or not Zn2+

is present

in the system. The repeated measurement gave the similar results. Thus, the equimolar Zn2+

addition

into DPA-DTC solution only trigger the disappearance of anodic peak at 0.3 V and the occurrence

of a new anodic peak at 1.7 V, which essentially reflects the energy level change of the HOMO of

DPA-DTC before and after adding Zn2+

.

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550 575 600 625

0

50

100

150

200

Wavelength (nm)

Rel

ati

ve

PL

Inte

nsi

ty

DPA-P-DTC-QDs+Zn2+

EDTA

Fig. S9 The re-quenching of the recovered PL of DPA-P-DTC-QDs suspension containing Zn2+

(16

M) upon the addition of EDTA (16 M).

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500 600 7000

1

2

3

N

orm

alized

PL

Inten

sityNorm

ali

zed

Ab

sorb

an

ce

Wavelength (nm)

0

1

2

3

Fig. S10 The normalized UV-vis and PL spectra (ex = 350 nm) of DPA-P-DTC-QDs in PBS (10

mM, pH 7.5).

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Table S1 Fluorescence lifetime data for OAm-capped CdSe/ZnS QDs and DPA-P-DTC-QDs in the

absence and presence of Zn2+

.

Substrate Emission lifetimes

a/ns Average lifetime

b

τav/ns τ1 τ2

OAm-capped CdSe/ZnS QDs 6.03 (51%) 24.31 (49%) 20.56

DPA-P-DTC-QDs 2.29 (77%) 8.31 (23%) 5.41

DPA-P-DTC-QDs + Zn2+

3.19 (44%) 15.65 (56%) 13.94 aThe PL decay was analyzed using the express F(t) = a1exp(-t/τ1) + a2exp(-t/τ2), where τ1

and τ2 were the lifetimes. The values in parentheses indicate the fraction (%) of the

corresponding lifetime component. bThe average lifetime values was calculated using the

expression τav = aiτi2/ aiτi.

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Table S2. Comparison of detection performance of various QDs-based probes for Zn2+

.

Linear range Detection limit Detection Probes References

0-20 M 0.8 M L-cysteine-capped CdS QDs 29b

5-500 M 2.4 M Azamacrocycle activated QDs 29c

10-1000 M 0.57 M CdSe/ZnS core/shell QDs-zincon conjugates 29d

1.6-35 M 1.2 M CdTe QDs 29e

0.3-15 M 0.08 M Mn2+

doped ZnS QDs 29f

0.2-5.0 mM No report Iminodiacetate-capped CdSe/ZnS core/shell QDs 29a

0.9-16 M 0.7 M DPA-P-DTC-QDs This work

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