ZnS Quantum Dots (QDs) on the Root Epidermis of

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The retention of CdS/ZnS quantum dots (QDs) on the root epidermis of woody plant and its implications by benzo[a]pyrene: Evidences from the in situ synchronous nanosecond time-resolved fluorescence spectra method Ruilong Li, Haifeng Sun, Shaopeng Wang, Yinghui Wang, and Kefu Yu J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b04258 • Publication Date (Web): 04 Jan 2018 Downloaded from http://pubs.acs.org on January 4, 2018

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Journal of Agricultural and Food Chemistry

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The retention of CdS/ZnS quantum dots (QDs) on the root epidermis of woody plant

2

and its implications by benzo[a]pyrene: Evidences from the in situ synchronous

3

nanosecond time-resolved fluorescence spectra method

4 5

Ruilong Li1,2,3, Haifeng Sun4, Shaopeng Wang1,2,3, Yinghui Wang1,2,3*, Kefu Yu1,2,3*

6 7

1

School of Marine Sciences, Guangxi University, Nanning 530004, P.R. China

8

2

Guangxi Laboratory on the Study of Coral Reefs in the South China Sea, Guangxi

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University, Nanning 530004, P.R. China

10

3

11

China

12

4

13

China

Coral Reef Research Center of China, Guangxi University, Nanning 530004, P.R.

College of Environment and Resource, Shanxi University, Taiyuan 030006, P.R.

14 15 16 17 18 19

*

20

University, Nanning 530004, P.R. China; Coral Reef Research Center of China,

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Guangxi University, Nanning 530004, P.R. China. E-mail: [email protected]

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(Yinghui Wang) and [email protected] (Kefu Yu)

Corresponding to: Yinghui Wang and Kefu Yu, School of Marine Sciences, Guangxi

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ACS Paragon Plus Environment


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Table of Contents Graphic

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25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 2


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Abstract

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The retention of CdS/ZnS QDs on the epidermis has been confirmed to be one of

44

core procedures during root uptake process. However, the retention mechanisms of

45

QDs on the epidermis of woody plant were poorly understood for lacking of

46

appropriate QDs quantitative method. In this study, a novel method for in situ

47

determination of CdS/ZnS QDs retained on the root epidermis was established using

48

synchronous nanosecond time-resolved fluorescence spectroscopy. No correlations

49

between Kf values of Oleylamine-CdS/ZnS QDs retained on the epidermal tissues and

50

the surface/bulk composition of mangrove root were observed (p> 0.05) due to the

51

existence of endocytosis mechanisms during the QDs uptake processes. Moreover, the

52

difference of the CdS/ZnS QDs in water and further translocated to xylem/phloem of

53

root rather than the combination with cell wall/membranes were the predominant

54

reason that caused the Kf values follow the sequence of PEG-COOH-CdS/ZnS QDs
A. corniculata

345

(0.41).

41

. These results

C-NMR data showed that the aliphatic carbon component accounted for 52.3 %,

346

It can be clearly seen that there exists no strong correlation between Kf-oc values

347

and the aromatic/aliphatic carbon of the bulk mangrove root with the coefficients (R2)

348

of 0.64/0.03 (table 2). These divergent findings reveal that it is necessary to further

349

probe

the

relationships

of

root

surface

polarity

16


and

the

retention

of

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42

350

Oleylamine-CdS/ZnS QDs. Fortunately, similar with the retention of PAHs

, the

351

Oleylamine-CdS/ZnS QDs retained on the epidermal tissues of mangrove root

352

ascends with the decreasing of the surface polarity ((N+O)/C) (table 2). However, no

353

strong negatively correlations were found between the (N+O)/C values and Kf-oc

354

values with coefficients (R2) of 0.22 (table 2). These two unexpected results indicated

355

that the existence of other Oleylamine-CdS/ZnS QDs transport or binding with root

356

epidermal tissues mechanisms made the compositions of mangrove root was not the

357

sole determination factor of the retention of Oleylamine-CdS/ZnS QDs.

358

As previously reported showed, no specific interactions including hydrogen

359

bonds and electrostatic attraction were existed between Oleylamine-CdS/ZnS QDs

360

and root cell/menbranes 43. Therefore, the existences of endocytosis, an invagination

361

of the cell membrane for the uptake of extracellular materials (nm), was likely to be

362

the reasons that the reduction of the correlations of Kf and chemical composition of

363

root. To confirm our assumption, the effects of temperature on the retention of

364

Oleylamine-CdS/ZnS QDs on the epidermal tissues were evaluated (figure S4).

365

Results showed that the retention of Oleylamine-CdS/ZnS QDs at 298.15 K were

366

markedly higher than 277.15 K (p< 0.05). Due to the passive apoplastic transport is a

367

non-metabolic, non-energy consuming process, the retention of Oleylamine-CdS/ZnS

368

QDs largely affected by temperature was an indicator that the transportation of this

369

compound including biochemically processes, which, as Kettiger et al pointed out 44,

370

was attributed to the apoplastic transport (refer the ‘‘Apoplastic versus symplastic

371

transport’’ section) or endocytosis.

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Another evidence for the presences of endocytosis that affects the retention of

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QDs on the epidermal tissues of mangrove root come from the images of FLIM

374

instrument,

375

Oleylamine-CdS/ZnS QDs (green, 15-25 ns) and auto-fluorescence signal of root (red

376

to yellow, < 10 ns) separately (Figure S5). In this figure, it can be clearly seen that

377

although the dominant concentrations of Oleylamine-CdS/ZnS QDs located on the

378

cell wall of epidermis, there still existed a small percentage of Oleylamine-CdS/ZnS

379

QDs distributed on the intracellular of roots epidermis. As previously reports shown,

380

the apoplastic transport (refer the ‘‘Apoplastic versus symplastic transport’’ section)

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or endocytosis were important pathways of neutrally QDs across the plant cell

382

wall/membrane and thus the phenomenon described above reconfirmed our

383

assumption

384

Oleylamine-CdS/ZnS QDs retained on the mangrove root epidermal tissues were

385

highly focused “stream” (aggregated) rather than patchily located in both longitudinal

386

and transverse directions.

which

was

suitable

to

display

the

fluorescence

signal

of

41

. In addition, similar as parent/alkyl/heterocyclic PAHs, the

387 388

3.3.2 The implications of charges of the QDs coating on its retained on the epidermal

389

tissues of mangrove root

390

Similar as Oleylamine-CdS/ZnS QDs, no positive/negative relationships were

391

obtained

between

the

Kf-oc

values

of

PEG-COOH-CdS/ZnS

392

PEG-NH2-CdS/ZnS QDs (Equilibrium time: 5 d) with different coating charges (The

393

zeta potentials of -4.3 mV, -21.6 mV and 17.1 mV for Oleylamine-CdS/ZnS QDs,

18


QDs

or

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394

PEG-COOH-CdS/ZnS QDs and PEG-NH2-CdS/ZnS QDs, respectively) and

395

aromatic/aliphatic carbon of bulk root/surface polarity with the corresponding

396

coefficients of 0.62/0.54/0.88 and 0.14/0.73/0.01 (table 2). More noteworthy was that

397

the retention of ZnSe/ZnS and PEG-NH2-CdS/ZnS QDs on the epidermal tissues did

398

not ascend with the decreasing of surface polarity of mangrove root. These results

399

indicated that the surface coating charge of CdS/ZnS QDs, aside from the chemical

400

composition of mangrove root, has potential ability to affect the retention of

401

PEG-NH2-CdS/ZnS QDs on the epidermal tissues of mangrove root.

402

As figure 3a showed, the Kf values of PEG- NH2-CdS/ZnS QDs on the epidermal

403

tissues of K. obovata root were 7.4 (ng/spot)/(ng Cd /mg)n, which was a little higher

404

than PEG-COOH-CdS/ZnS QDs (p> 0.05) but much lower than Oleylamine-CdS/ZnS

405

QDs (p< 0.05). Similar results were obtained for A. marina and A. corniculata. Both

406

of the cationic and anionic coating QDs easily dissolved in water and then majority of

407

these kinds of QDs transport to the xylem/phloem tissues through root water and

408

nutrients absorption pathways instead of retaining on the epidermal tissues 45, which

409

leading to the Kf values of cationic and coating QDs much smaller than

410

Oleylamine-CdS/ZnS QDs. Besides, the strong electrostatic attraction of positive

411

charged QDs coating and the negatively charged root cell wall made the retention of

412

PEG-NH2-CdS/ZnS QDs a little higher than PEG-COOH-CdS/ZnS QDs

413

Overall, in this study, multi-factors, including the root composition, endocytosis

414

and surface coating charges of CdS/ZnS QDs, were confirmed to be the factors that

415

affect the retention of CdS/ZnS QDs on the epidermal tissues of mangrove root.

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416 417

3.4 The implications of B[a]P on the retention of CdS/ZnS QDs on the epidermal

418

tissues of mangrove root

419

The implications of PAHs on the retention of PEG-NH2-CdS/ZnS QDs on the

420

epidermal tissues were displayed in figure 3b and 3c. The lower concentrations of

421

B[a]P exposures (100 µg/L) inhibited the retention of PEG-NH2-CdS/ZnS QDs on the

422

epidermal tissues of K. obovata root, with the Kf values decreased to 4.8

423

(ng/spot)/(ng Cd /mg)n at 298.15 K. On the contrary, there existed almost no

424

differences for the retained concentration of Oleylamine-CdS/ZnS QDs and

425

PEG-COOH-CdS/ZnS QDs with and without the presence of B[a]P (p>0.05). Similar

426

results were also obtained for A. marina and A. corniculata. When low concentrations

427

of phenanthrene were presented, Yin et al confirmed that the depolarization of root

428

membrane potential was obvious, and the magnitude of depolarization is in good

429

accordance with the phenanthrene concentration uptake by root 24. Thus, the attractive

430

force between the positively charged PEG-NH2-CdS/ZnS QDs located on the root

431

surface and negatively charged root cell wall and membranes were weakened, which

432

lowers the retention of PEG-NH2-CdS/ZnS QDs on the epidermal tissues of mangrove

433

root. Meanwhile, the other physiological statuses of root did not affected by PAHs and

434

the retained concentrations of Oleylamine-CdS/ZnS QDs and PEG-COOH-CdS/ZnS

435

QDs kept constant.

436

However, it should be noted that the Kf values of PEG-NH2-CdS/ZnS QDs retained

437

on the epidermal tissues decreased to 3.1, 2.5 and 2.0 (ng/spot)/(ng Cd /mg)n for K.

20


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438

obovata, A. marina and A. corniculata, respectively, while the phenomenon was also

439

an observer for Oleylamine-CdS/ZnS QDs and PEG-COOH-CdS/ZnS QDs at high

440

B[a]P concentrations (500 µg/L, 298.15 K). Despite the depolarization of root

441

membrane potential that inhibited the retention of PEG-NH2-CdS/ZnS QDs, as was

442

reported by Dupuy et al

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endodermis of woody plant largely increased the possible adsorption sites for

444

Oleylamine-CdS/ZnS QDs and PEG-COOH-CdS/ZnS QDs with the neutrally and

445

negatively charge after 7 d exposure.

25

, the extensive deposition of suberin on exodermis and

446

In this study, the S-NSFS method were established, which detection limits can

447

reach as low as 1.2-2.0 ng/spot for the three kinds of CdS/ZnS QDs, providing a novel

448

approach for sensitive and accurately in situ determination of trace concentration of

449

the CdS/ZnS QDs retained on the epidermal tissues of root. More importantly, our

450

studies firstly confirmed that the retention of CdS/ZnS QDs on the epidermal tissues

451

was determined by multi-factors, which includes the composition of mangrove root,

452

the endocytosis and the charge of the CdS/ZnS QDs coating, and further work showed

453

that this fraction of CdS/ZnS QDs were largely affected by the PAHs in root. Overall,

454

the findings of this work may be helpful in understanding the role of epidermal tissues

455

in the uptake of CdS/ZnS QDs by woody plants.

456 457

Supporting Information

458

The nanosecond time resolved fluorescence spectra of different kinds of QDs at

459

optimal emission wavelength; The NSFS of the Oleylamine-CdS/ZnS QDs retained

21



460

on the epidermal tissues of K. obovata root with the presence of B[a]P after filter out

461

< 10 ns fluorescence signal (Figure S2); The rates of QDs retained on the epidermal

462

tissues of mangrove root (Figure S3); The partition coefficients (Kf) of the QDs

463

retained on the epidermal tissue of mangrove root at two different temperatures

464

(Figure S4); The FLIM images of Oleylamine-CdS/ZnS QDs retained on the

465

epidermal tissue of mangrove root (Figure S5); Results of recovery experiment for the

466

CdS/ZnS QDs retained on the epidermal tissues of mangrove root (Table S1);

467

Integration results from

468

Surface functionalities of the epidermal tissue of mangrove root acquired by XPS

469

(Table S3)

13

C-NMR of different kinds of mangrove roots (Table S2);

470 471

Acknowledgments

472

The authors are grateful for financial support from the Natural Science

473

Foundation of China (No. 91428203, No. 21507077, No. 41673105, No. 41273139)

474

and the BaGui Scholars Program Foundation (2014).

475 476

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(a)

(b)

Fig. 1 The emission fluorescence spectra of 100 ng/spot Oleylamine-CdS/ZnS QDs on the epidermal tissues of mangrove root with (a) and without (b) filter the short lifetime auto-fluorescence signal (< 10 ns).

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5

1

Fig. 2. The S-NSFS of the Oleylamine-CdS/ZnS QDs retained on the epidermal tissues of K. obovata root with the presence of B[a]P after filters out the short-lived fluorescence signals (< 10 ns). Concentrations of Oleylamine-CdS/ZnS QDs adsorbed from 1-5 were 100, 200, 300, 400 and 550 ng/spot, respectively.

27



(a)

(b)

(c)

Fig. 3. The partition coefficients (Kf) of the CdS/ZnS QDs retained on the epidermal tissue of mangrove root (a) without B[a]P and (b) 100 µg/L B[a]P (c) 500 µg/L B[a]P.

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Table 1. Analytical merits of the established method. Detection limita

Linear range Mangrove

QDs

Calibration curve

Correlation coefficient (ng/spot)

K. obovata

A. marina

A. corniculata

a

(ng/spot)

Oleylamine-CdS/ZnS

yb=9.2xc+127

15.5-2100

0.9826

1.5

PEG-COOH-CdS/ZnS

y=20.3x+101

21.0-3310

0.9711

1.2

PEG-NH2-CdS/ZnS

y=12.1x+203

34.5-1970

0.9909

2.0

Oleylamine-CdS/ZnS

y=14.7x+314

20.0-2700

0.9940

1.1

PEG-COOH-CdS/ZnS

y=22.6x+148

35.5-1700

0.9832

1.3

PEG-NH2-CdS/ZnS

y=15.5x+262

40.0-1260

0.9917

1.7

Oleylamine-CdS/ZnS

y=18.4x+186

15.5-4200

0.9944

1.5

PEG-COOH-CdS/ZnS

y=14.2x+210

28.5-1460

0.9809

1.8

PEG-NH2-CdS/ZnS

y=15.3x+226

36.0-2410

0.9922

1.6

detection limit of the method, which was calculated by 3SB/m, where ‘SB’ is the standard deviation of the blank, and ‘m’ is the slope of the calibration curve; b y

represents the S-NSFS intensity of CdS/ZnS QDs adsorbed onto the epidermal tissue of mangrove root. c x represents the concentrations of CdS/ZnS QDs adsorbed onto the epidermal tissue of mangrove root.

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Table 2 The correlation coefficients between the retained concentration of QDs and surface (O+N)/C or bulk compositions (aromatic carbon and aliphatic carbon) of mangrove root. QDs

Oleylamine-CdS/ZnS

PEG-COOH-CdS/ZnS

PEG-NH2-CdS/ZnS

a

Mangrove

Kf-oca

K. obovata

72.2

A. marina

74.5

A. corniculata

118.3

K. obovata

35.3

A. marina

24.1

A. corniculata

31.9

K. obovata

31.2

A. marina

23.9

A. corniculata

31.7

Fitting equation (S) b

R(S)2

Fitting equation (B) c

R(B)2

Fitting equation (A) d

R(A)2

ye=-0.0063xf+0.2859

0.22

y=-0.7117x+44.892

0.64

y=-0.0537x+55.844

0.03

y=-0.0023x+0.6803

0.62

y=-0.1451x+36.073

0.54

y=0.0712x+47.809

0.88

y=0.0075x+0.2659

0.14

y=-1.1383x+55.408

0.73

y=-0.0323x+55.013

0.01

Mean value of Kf-oc of six measurements, the units of Kf-oc was (ng/spot)/(ng Cd /mg)n; b Fitting equation (S) and R(S) represent the fitting equations and correlation

coefficient between Kf-oc value of CdS/ZnS QDs. and surface (O+N)/C, respectively; c Fitting equation (B) and R(B) represent the fitting equations and correlation coefficient between Kf-oc value of CdS/ZnS QDs. and aromatic carbon content of bulk root, respectively d Fitting equation (A) and R(A) represent the fitting equations

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and correlation coefficient between Kf-oc value of QDs. and aliphatic carbon content of bulk root, respectively; e y represents the value of surface polarity ((O+N)/C), bulk aromatic carbon or aliphatic carbon content of epidermal tissue of mangrove root; f x represents the Kf-oc value of QDs.

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ZnS Quantum Dots (QDs) on the Root Epidermis of

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