Skin color-specific and spectrally-selective naked-eye dosimetry of UVA, B and C radiations

Wenyue Zou,1 Ana González,2 Deshetti Jampaiah,1 Rajesh Ramanathan,1 Mohammad Taha,3 Sumeet Walia,3 Sharath Sriram,3

Madhu Bhaskaran,3 José M. Dominguez-Vera2,* and Vipul Bansal1,*

1Ian Potter NanoBioSensing Facility, NanoBiotechnology Research Laboratory, School of Science, RMIT University, Melbourne, Australia.2Departamento de Química Inorgánica, Universidad de Granada, Granada, Spain.3Functional Materials and Microsystems Research Group and Micro Nano Research Facility, RMIT University, Melbourne, Australia.

Introduction

Development of the photoactive ink

PMA control

Malonic acid

Acetic acid

Glycine

Methanol

Alanine

Ethanol

Ethylene alcohol

Oxalic acid

Glycolic acid

Lactic acid

0.0

0.2

0.4

0.6

0.8

1.0

1.2

Electron donor

UVA

UVB

UVC

A700

nm

Electron donor

Ab

so

rban

ce a

t 700

nm

0 10 20 30

0.0

0.4

0.8

1.2

Ab

so

rban

ce a

t 700 n

m

UV irradiation time / min

➢ Selection of the ink components ➢ Selection of the ink composition

0 20 40 60 80 100

0.0

0.5

1.0

1.5

2.0 UVA

UVB

UVC

0 20 40 60 80 100

0.0

0.5

1.0

1.5

2.0 UVA

UVB

UVC

PMA 1 mM

Ab

so

rban

ce a

t 700 n

m

Molar ratio (LA:PMA)

0 20 40 60 80 100

0.0

0.5

1.0

1.5

2.0 UVA

UVB

UVC

PMA 2.5 mM PMA 5 mM

Comparison of the ability of different e– donorsin reducing phosphomolybdic acid (PMA) onexcitation with UVA, B and C for 30 min.

Inset: UVR exposure time-dependent responseof PMA in the presence of lactic acid (LA).

Concentration: PMA 1 mM; e– donor 10 mM.UVR intensity: 15 W·m–2.

Influence of the concentration of PMA 1 mM,2.5 mM, and 5 mM, and LA:PMA Molar ratioson sensor response measured from absorbanceat 700 nm after exposing samples for 5 min.

UVR intensity: 15 W·m–2.

UV exposure limit for people with different skin color

Skin type I II III IV V VI

Skin color

Very fair Fair Medium Olive Brown Dark brown

MED

UVB

(J•m–2)200-300 250-350 300-500 450-600 600-1000 1000-2000

UVA

(J•m–2)200-350

(x103)

300-450

(x103)

400-550

(x103)

500-800

(x103)

700-1000

(x103)

>1000

(x103)

Minimal erythemal dose (MED) is defined as the lowest threshold dose that may produce sunburn.

Ultrasensitive UV sensing in solution-based system

Ab

so

rban

ce a

t 700 n

m

a

b

c

d

10 100 10000.0

0.1

0.2

0.3

0.4

A7

00

nm

UV dose / J/m2

UVA

UVB

UVC

Pre

cis

ion

/ %

0 300 600 900 12009596979899

100

UVC

0 300 600 900 12009596979899

100

UVB

0 300 600 900 12009596979899

100

UVA

UV dose / J•m–2 UV dose / J•m–2

(a) UVR dose-dependent colorimetricresponse of PMA-LA photoactive inkdemonstrating the sensor’s ability todifferentiate UVA, B and C even atextremely low dosages, as reflectedfrom logarithmic X-axis. The highlightedresponses correspond to the UVB MEDfor type I to VI skin.

Each data point represents an averageof colorimetric response obtained from12 independent sensors and associatedstandard deviation.

(b-d) Precision of PMA-LA sensors ateach of the UV doses at 10 J·m–2

increments, as calculated from the datapresented in (a).

Naked-eye UV detection on paper-based system

0 9000 1800097

98

99

100

200 400 600 800

20

40

60

80

200 400 600 800

20

40

60

80

0 9000 1800097

98

99

100

10 100 1000 10000 100000

60

70

80

90

100 UVA

UVB

UVC

0 9000 1800097

98

99

100

Time (s) 0 5 10 20 30 40 50 60 90 120 200 300 600 900 1800 3600

0 25 50 100 150 200 250 300 450 600 1000 1500 3000 4500 9000 18000UV dose

(J·m–2)

UVA

UVB

Wavelength / nm

Refl

ecta

nce /

%

Rela

tive r

efl

ecta

nce /

%

Pre

cis

ion

/ %

UVA

UVB

UVC

a

b

c

d

f

g

he

200 400 600 800

20

40

60

80

UVA

UVB

UVC

UVC

UV dose / J•m–2 UV dose / J•m–2

(a) Photographs of three paper-based UVsensors with increasing exposure time andcorresponding cumulative effective doseof UVA, B, and C. The sensor response atthe UVB MED doses of skin types I-VI ishighlighted.

(b-d) Reflectance spectra of smileys onexposure to UVA, B, and C, respectivelywith increasing UVR doses.

(e) UVR dose-dependent responseshowing PMA-LA smiley sensor’s ability todifferentiate UVA, B and C even atextremely low dosages.

(f-h) Precision of PMA-LA smiley sensors ateach of the tested UV doses, as calculatedfrom the data presented in (e).

Skin type I, MED 200 J∙m-2 Skin type II, MED 250 J∙m-2

63

125

188

250

0

50

100

150

200

0

TFF layers

0 1 2 3 0 2 3 4

TFF layers

UV

B d

os

e (J•m

-2)

25%

50%

75%

100%Inc

rea

sin

g s

ola

rU

V d

ose MED

UV

B d

os

e (J•m

-2)

Skin type III, MED 300 J∙m-2

75

150

225

300

0

0 2 4 5

TFF layers

UV

B d

os

e (J•m

-2)

Skin type IV, MED 450 J∙m-2

113

225

338

450

0

1 4 5 6

TFF layers

UV

B d

os

e (J•m

-2)

25%

50%

75%

100%Inc

rea

sin

g s

ola

rU

V d

ose

MED

Skin type V, MED 600 J∙m-2 Skin type VI, MED 1000 J∙m-2

250

500

750

1000

0

150

300

450

600

0

2 5 6 7 4 6 7 8

TFF layers TFF layers

UV

B d

os

e (J•m

-2)

UV

B d

os

e (J•m

-2)

PMA Lactic acid PMAreduced Pyruvic acid

PMA-LA

mixture as an

invisible ink on

filter paper

Colorless Blue color

Incre

asin

g s

ola

r U

V d

ose

a

UV light

b

Coating of

transparency

films as optical

filters (TFF)

c

Decreasing UV transmittance

d

Solar UV

exposure

Appearance of blue smileys

Design of the paper-based solar UV dosimeters

The sun’s ultraviolet radiation (UVR) is both the main cause of skin cancer and the best natural source for vitamin D.

UVR is classified into UVA, UVB and UVC. They can cause remarkably different effects on biological entities.

People with different skin phototypes have diverse levels of UV tolerance.

UVR is neither visible to humans nor related to temperature. Therefore, people are not able to see or feel UVR.

UVRis important.

UVR monitoring technology is needed.

Spectrally-selective UVR monitoring is required.

Customized skin color-specific and spectrally-selective UVR monitoring system for practical mass usage

is in demand.

PMA + LA 5 mM PMA + 300 mM LA

(a) The aqueous solution containing PMA is reducedby UVR in the presence of LA to produce a blueproduct.

(b) The PMA-LA mixture acts as an invisible ink to pen-draw four smileys on a strip of filter paper.

(c) These smileys are coated with increasing numberof transparency film filters (TFF) that increasinglyreduce the UV transmittance on smileys from left toright.

(d) After solar UV exposure, blue smileys start toappear on the paper strip sensor from left to right,such that the appearance of 1 to 4 blue smileysrepresents 25, 50, 75 and 100% of safe exposurethresholds, respectively.

Customized skin color-specific UV dosimeters

Performance of six customizedsensors in simulated solar light,assuring that sensors meet thewide-ranging UVB MED thresholdsof people with different skin colors.The skin-phototype specificity isachieved by an appropriatecombination of the smiley paperdiscs coated with different TFF layers(0–8) in a single sensor that allowsdose-dependent modulation ofsensor response.

Conclusion✓ Ease in fabrication due to a simple printable ink and readily-available low-cost household components;

✓ Paper-based sensors offering multi-format wearable potential;

✓ High spectral selectivity allowing UVA, B and C selective monitoring;

✓ High sensitivity allowing naked-eye dosimetry without the requirement of a technological interface;

✓ Robust sensors with high specificity, durability and stability across different environmental conditions;

✓ Customisable for people with different skin phototypes.

0 1500 3000 4500

60

70

80

90

100

Untreated

Visible light treated

IR light treated

50 oC heat treated

RH 90% treated

Re

lati

ve

re

fle

cta

nc

e / %

UV dose / J•m–2

0 1500 3000 4500

60

70

80

90

100

15 % RH / 50 oC

27 % RH / 30 oC

45 % RH / 22 oC

60 % RH / 21 oC

75 % RH / 20 oC

90 % RH / 19 oC

0 1500 3000 4500

60

70

80

90

100 0-week

2-week

4-week

6-week

8-week

a b c

High durability and stability

AcknowledgementAuthors acknowledge the Australian Research Council (ARC) for supporting this work through Future Fellowship (FT140101285 – V.B.)and Discovery schemes (DP170103477 – V.B. and R.R.). V.B. acknowledges the generous support of the Ian Potter Foundation inestablishing Sir Ian Potter NanoBioSensing Facility at RMIT University. W.Z. acknowledges RMIT University for the Vice Chancellor’spostgraduate scholarship; R.R. and S.W. acknowledge RMIT University for Vice Chancellor‘s Postdoctoral Fellowships; V.B. and M.B.thanks ARC for a Future Fellowships and a DECRA Fellowship, respectively. J.M.D. acknowledges the Commonwealth of Australia foran Endeavour Executive Award towards a sabbatical at RMIT University.

(a) The paper-based UV sensors show high durability after pre-exposing them to different ambient-mimicking environmental conditions for one hour. (b) The paper-based UV sensors show stable UVB sensing performance while simultaneously exposing them to a wide range of relative humidity and ambient temperature conditions. (c) The PMA-LA ink employed to prepare smiley sensors remains stable for at least over 8 weeks