High-performance bio-piezoelectric nanogenerator made with fish scaleSujoy Kumar Ghosh and Dipankar Mandal Citation: Applied Physics Letters 109, 103701 (2016); doi: 10.1063/1.4961623 View online: http://dx.doi.org/10.1063/1.4961623 View Table of Contents: http://scitation.aip.org/content/aip/journal/apl/109/10?ver=pdfcov Published by the AIP Publishing Articles you may be interested in Performance optimization of p-n homojunction nanowire-based piezoelectric nanogenerators through control ofdoping concentration J. Appl. Phys. 118, 094307 (2015); 10.1063/1.4930031 Self-amplified piezoelectric nanogenerator with enhanced output performance: The synergistic effect ofmicropatterned polymer film and interweaved silver nanowires Appl. Phys. Lett. 106, 163901 (2015); 10.1063/1.4918986 Piezoelectric nanogenerator based on zinc oxide nanorods grown on textile cotton fabric Appl. Phys. Lett. 101, 193506 (2012); 10.1063/1.4766921 Measured efficiency of a ZnO nanostructured diode piezoelectric energy harvesting device Appl. Phys. Lett. 101, 093902 (2012); 10.1063/1.4749279 Probing the effect of relative molecular orientation on the photovoltaic device performance of an organic bilayerheterojunction using soft x-ray spectroscopies Appl. Phys. Lett. 100, 263302 (2012); 10.1063/1.4731197

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High-performance bio-piezoelectric nanogenerator made with fish scale

Sujoy Kumar Ghosh and Dipankar Mandala)

Organic Nano-Piezoelectric Device Laboratory (ONPDL), Department of Physics, Jadavpur University,Kolkata 700032, India

(Received 21 June 2016; accepted 11 August 2016; published online 6 September 2016)

Energy harvesting performance of an efficient flexible bio-piezoelectric nanogenerator (BPNG) is

demonstrated, where “bio-waste” transparent fish scale (FSC), composed of self-assembled and

ordered collagen nano-fibrils, serves as a self-poled piezoelectric active component, exhibiting

intrinsic piezoelectric strength of �5.0 pC/N. The dipolar orientation (�19%) of the self-polarized

FSC collagen is confirmed by the angular dependent near edge X-ray absorption fine structure spec-

troscopy. The BPNG is able to scavenge several types of ambient mechanical energies such as

body movements, machine and sound vibrations, and wind flow which are abundant in living envi-

ronment. Furthermore, as a power source, it generates the output voltage of 4 V, the short circuit

current of 1.5 lA, and the maximum output power density of 1.14 lW/cm2 under repeated com-

pressive normal stress of 0.17 MPa. In addition, serially integrated four BPNGs are able to produce

enhanced output voltage of 14 V that turn on more than 50 blue light emitting diodes instantly,

proving its essentiality as a sustainable green power source for next generation self-powered

implantable medical devices as well as for personal portable electronics with reduced e-waste ele-

ments. Published by AIP Publishing. [http://dx.doi.org/10.1063/1.4961623]

Energy harvesting from vibrations in the living environ-

ment is an effective approach for “battery-free” self-powered

devices or nanogenerators (NGs). This is the key requirement

for the realization of the fully independent and sustainable

operation of low power-consuming devices and systems.1,2 To

date, some attractive approaches based on piezoelectric3,4 and

triboelectric5 NGs have been proposed for the conversion of

mechanical movements into electrical power. However, to uti-

lize the NGs as an eco-friendly and feasible energy harvester

in practical life, there are several issues, such as initial toxic

compounds for synthesis, harsh conditions and/or complex

fabrication steps, and cost factor that need to be addressed.6 In

this context, the natural piezoelectric materials, such as colla-

gen fibrils,7,8 hydroxyapatite,9 and cellulose10 which are also

known as eco-friendly materials, are the suitable choices for

designing bio-piezoelectric nanogenerator (BPNG). Among

them, the most abundant piezoelectric biomaterial present in

animal tissues such as skin, tendon, cartilage, bone, and even

in human heart, is the type I collagen, which is a biocompati-

ble and biodegradable polymer enabling fabrication of the

flexible BPNG.11 The cost effective collagen source is the fish

constituents such as skin, fins, maws, and swim bladder which

are mainly treated as “bio waste” materials because different

fish species are consumed daily in large quantities world-

wide.12,13 The disposal of these bio-wastes causes an increas-

ing environmental pollution. The recycling of the fish by-

products into the BPNG via one step process is a promising

solution for the development of value-added products and

also to reduce the e-waste elements. It is noteworthy that col-

lagen consists of three polypeptide chains (a-chain) with two

identical a1(I) chains and a different a2(I) chain. Each

a-chain is composed of repeated triplet amino acid motif

sequence of Gly (Glycine)-X-Y, where X and Y are often pro-

line (Pro) and hydroxyproline (Hyp), respectively. The three

a-chains twist together into a unique triple-helical structure to

form tropocollagen. The quarter staggered arrangement of

collagen molecules contributes to collagen fibrils with a char-

acteristic axial periodic structure, and the fibrils further assem-

ble into a collagen fiber.14,15 The intrinsic presence of polar

uniaxial orientation of hydrogen bonding motifs between the

polypeptide chains acts as molecular dipoles that cause spon-

taneous polarization and piezoelectricity. It causes the colla-

gen to become a natural electret or bioelectret material as

well.16 To date, there are very few initiatives to explore the

mechanical energy harvesting performance of biomateri-

als.17,18 However, the bio-waste fish scale (FSC) has not been

applied as piezoelectric power generator until now.

Herein, a simple, cost-effective and one-step approach is

initiated where bio-waste FSC was chosen to make an ultra-

sensitive BPNG. To fabricate the BPNG, FSCs (Figure 1(a))

(of Catla catla, a sweet water fish) were collected from the

fish processing market and washed thoroughly with deionised

water followed by a solvent system of NaOH, 1.0 M NaCl,

FIG. 1. Fabrication of flexible BPNG from bio-waste FSC. (a) Photograph

of the bio-waste raw FSC. Digital photographs of the demineralised FSC,

showing transparency and flexibility (by rolling) (in the insets). (b) The flex-

ibility of the BPNG is shown by human fingers. (c) The schematic diagram

of BPNG showing the simple structure of the device.

a)Author to whom correspondence should be addressed. Electronic mail:

dipankar@phys.jdvu.ac.in. Tel.: þ91-94333-73530, Fax: þ91-33-2413-

8917.

0003-6951/2016/109(10)/103701/5/$30.00 Published by AIP Publishing.109, 103701-1

APPLIED PHYSICS LETTERS 109, 103701 (2016)

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12:40:10

0.05 M Tris HCl, and 20.0 mM EDTA. Finally, the FSCs were

immersed in a solution of 0.5 M EDTA to obtain transparent

and flexible demineralised FSCs (thickness �250 6 10 lm).

Therefore, after demineralisation, the collagen layers serve as

active piezoelectric element in the resulting FSC which is not

only transparent (�34% to 46% transparency) (upper inset of

Figure 1(a) and supplementary Figure S1) but also rollable

(lower inset of Figure 1(a)) that makes suitable to a flexible

BPNG (Figure 1(b)). To fabricate the robust BPNG, we have

made the gold electrodes of 90 nm thickness on both sides of

FSC by sputtering followed by lamination with polypropylene

(PP) film (of thickness �125 lm). The simple structure of

BPNG is illustrated in Figure 1(c). The presence of self-

assembled well-aligned collagen nano-fibrils (diameter ca.

40 nm) is revealed from the FE-SEM image (Figure 2(a)). The

banded pattern collagen nano-fibrils with D-periodicity of

62 6 4 nm (inset of Figure 2(a)) affirmed that the polypeptide

chains are packed together in a self-organized manner with

native helical conformation.

The presence of amino acids in the triple helix structure of

the polypeptide chains is confirmed by Raman spectroscopy

(Figure 2(b)). For example, the band arises at 1671 cm�1 due

to stretching (�) vibration of carbonyl group (� (C¼O))

of peptide backbone in Gly-X-Y tripeptide sequence, attrib-

uted to amide I band.14 The strong absorbance at 1456 cm�1

corresponds to the CH2 deformation (d (CH2)). The vibra-

tional bands arise at 1279 cm�1 and 1250 cm�1 due to in plane

deformation of N-H (d(N-H)) coupled to C-N stretching mode

(�(C-N)), respectively, ascribed to amide III band. This band

signifies the polar triple helix structure of collagen.19,20

Additionally, bands corresponding to carboxyl groups (such as

at 1432 cm�1 from aspartic acid and 1060 cm�1 from glutamic

acid) and protonated amino residues, i.e., NH3þ (1110 cm�1),

are also observed. The region of 1000–800 cm�1 in the spectra

is very much significant where amino acids such as

Phenylalanine (1037 and 1007 cm�1), Proline (Pro) (917 and

855 cm�1), and Hydroxyproline (Hyp) (881 cm�1) show strong

Raman scattering due to aromatic or saturated side chain rings.

The peak at 942 cm�1 represents the C-C stretching (�(CC))

vibration of the peptide backbone. Thus, Raman spectrum con-

firms the presence of helical structure in collagen of FSC with

the tripeptide sequence of Gly-Pro-Y and Gly-X-Hyp.14,19–22

The presence of amide II band (which is Raman inactive) in

collagen nano-fibrils is confirmed by the FT-IR spectrum (sup-

plementary material, Figure S2). The purity of collagen nano-

fibrils is also examined by the UV-vis spectroscopy (supple-

mentary material, Figure S3). The highly stable crystalline

structure of polypeptide chains of collagen nano-fibrils is con-

firmed via X-ray diffraction (XRD) analysis (Figure 2(c)). The

peak arising at 2h � 8:8� signifies the compact intermolecular

lateral packing structure of collagen nano-fibrils with d spacing

of 1.0 nm. A broad diffraction pattern arises from the amor-

phous components of FSC. In addition, the linear translational

length (d � 0:283 nm) per amino acid in a single a-chain

FIG. 2. (a) FE-SEM image of FSC

with histogram profile of D-periodicity

in the inset. (b) Raman spectrum in the

range of 1800–800 cm�1. (c) XRD pat-

tern in the region of 2h � 5:5� 70�.(d) Angular dependent O K-edge

NEXAFS spectra. The inset shows the

incident beam geometry with respect

to FSC. (e) Polarization vs. electric

field (P-E) curve and (f) corresponding

strain vs electric field (es-E) of the FSC

under an electric field of 6200 kV=cm

at 1 kHz.

103701-2 S. K. Ghosh and D. Mandal Appl. Phys. Lett. 109, 103701 (2016)

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12:40:10

along triple helix structure of the collagen is determined from

the deconvoluted peak at 2h � 31:6�.Furthermore, the axial translation length in amino acid

residues in the N (d � 0:224 nm) and C (d � 0:207 nm) ter-

minal telopeptides is obtained from the deconvoluted peaks

at 2h � 40:2� and 43:7�, respectively.21,22 In addition, it is

important to identify the alignment of molecular dipoles

(–CONH hydrogen bonding motifs) in the polypeptide

chains in order to investigate the origin of piezoelectricity in

FSC. Thus, angular dependent (30� and 90�) near edge X-ray

absorption fine structure (NEXAFS) spectroscopy was

employed (Figure 2(d)) by measuring the total electron yield

(TEY).23 The Lorentzian type sharp resonance peak at

531.6 eV has been observed in the O K-edge spectra (Figure

2(d)) due to O 1s ! p�CONH transition.24 Also, the spectra

manifest the broad feature of hydroxyproline due to r�ðO� CÞtransition.25 Interestingly, the spectra revealed significant

differences in the intensity of p�CONH resonant peak under dif-

ferent incidence angles (30� and 90�) of polarized X-ray pho-

ton, indicating the presence of oriented dipoles. This change

in peak intensity is attributed to X-ray linear dichroism phe-

nomena.23 The degree of molecular alignment in the FSC is

determined from the linear dichroism (P) expressed as

P ¼IEk � IE?

IEk þ IE?

� 100%; (1)

where IEk and IE? are the maximum of p�CONH resonance

intensities for the field vector Ek (at angle, h� 90�) and E?(at angle, h� 30�), respectively, determined from the angle

between ~E of the incident X-ray photon and macromolecular

axis of collagen in FSC.23,26 We have found very strong

degree of molecular alignment (�19%) of –CONH hydrogen

bonding motif in the FSC, thus treated as a self-polarized

one. Besides this, the dielectric constant (er � 154 at 1 kHz)

and loss tangent (tan d� 2.07 at 1 kHz) over a wide range of

frequency (100 Hz to 1 MHz) (supplementary material,

Figure S4a) suggest a good insulating property of FSC. The

sudden increase of er and tan d in the low frequency region

(1 kHz to 100 Hz) is mainly influenced by trapping of free

charges present in the large number of interfaces between

fibers and air pores that primarily constitute the collagen net-

works in FSC. It is well known as Maxwell–Wagner–Sillars

(MWS) interfacial polarization effect. Other secondary pro-

cesses may also play the role due to the ionic movements

and hydrogen bonds bound to the protein structure.27 The

FSC exhibits a good ferroelectric property with the remnant

polarization (Pr) of 0.29 lC/cm2 as revealed from Figure

2(e). Furthermore, the mechanical strain response under the

electric field (known as converse piezoelectric effect) is

demonstrated by the symmetrical butterfly shaped strain–

electric field (es-E) hysteresis loop (Figure 2(f)), where maxi-

mum 0.08% of longitudinal strain was found. The relation-

ship between es and P is given by

es ¼ QcP2; (2)

where the proportional coefficient Qc is the charge-related lon-

gitudinal electrostrictive coefficient. The plot of es versus P2 is

nearly a straight line (supplementary material, Figure S4b),

yielding the magnitude of Qc¼ 0.47 m4/C2 which is more than

fifteen times greater than the conventional inorganic piezoelec-

tric materials, e.g., BaTiO3 and PZT ceramics.28,31 Thus, the

adequate signature of piezoelectricity in the FSC is stemmed

from the remnant polarization in the P-E loop because longitu-

dinal piezoelectric charge coefficient (d33) follows the Pr value

(according to the macroscopic dimensional effect).29–31 In our

study, the experimentally measured d33 value (��5:0 pC=N)

(supplementary material, Figure S5) is in very close agreement

with the theoretical calculation (supplementary material,

Associate discussion S1). The ferroelectricity in FSC arises

due to flips of the polar –CONH hydrogen bonding motifs

(supplementary material, Figure S4c) present in the collagen

crystal of FSC.7,11,15,16 As a result, well-aligned, regular out-

of-plane polarization domains are formed due to appearance of

the spontaneously polarized state. The enhanced polarization

in the FSC resulting from the cooperative electromechanical

mutual interaction among the well-aligned adjacent collagen

nano-fibrils during compressive stress, called Maxwell stress,

generated when a high electric field is applied, compared to a

single fiber.8 Interestingly, this behaviour is observed without

any prior electric poling treatment, and thus, FSC is attributed

as a bioelectret material.16 Consequently, possessing the intrin-

sic d33, FSC is expected to provide piezoelectric output without

post-poling technique that might be well suited for the fabrica-

tion of BPNG.

The BPNG is able to convert several forms of mechani-

cal energy into electricity. For example, gentle press-hold-

release motions of single human finger (i.e., under uniaxial

compressive stress of amplitude (ra) �3.75 kPa and strain

rate of 0.017% s�1) (supplementary material, Associated dis-

cussion S2, Tables S1 and S2, where theoretical calculation

is also given) results in the output voltage (�680 mV) with

perfect switching of polarity (supplementary material, Figure

S5a and Associated discussion S3). In addition, it harvests

vibrational energy during walking and running conditions

(supplementary material, Figure S6b and Associated discus-

sion S3). Furthermore, BPNG scavenges mechanical energy

from high level vibration, such as machine vibration (supple-

mentary material, Figure S6c and Associated discussion S3)

and also from very low level vibration, arises from sound

(e.g., ra � 0.2–2.0 Pa by music) and wind motions (e.g., air

flow, �3.6 m/s) (supplementary material, Figure S6d,e and

Associate discussion S3). To investigate the suitability of the

BPNG as energy harvesting power source, it was imparted

repeatedly by hand slapping (Figure 3(a)) as reported ear-

lier.10,29 The periodical impact of ra� 0.17 MPa with 0.77%

s�1 strain rate (supplementary material, Associate discussion

S2) generates the rectified open circuit voltage (Voc) of 4 V

(Figure 3(b)) which is quite stable over large cycles (supple-

mentary material, Figure S7) and short circuit current (Isc) of

1.5 lA (supplementary material, Figure S8a). The sensitivity

of BPNG is 23.5 lV Pa�1. The integral of a single cycle of Isc

(supplementary material, Figure S8b) gives the charge value

(Qe) of 213 pC generated under the applied force (F) of 37.6 N

(supplementary material, Table S2) where Qe is given as

Qe ¼ð

Iscdt: (3)

103701-3 S. K. Ghosh and D. Mandal Appl. Phys. Lett. 109, 103701 (2016)

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12:40:10

Thus, the quasi-static piezoelectric coefficient17,32 is evalu-

ated as d33¼Qe/F¼ 5.6 pC/N, which is in close agreement

with the calculated (d33� 5.5 pC/N) as well as the directly

measured (d33� 5.0 pC/N) value. Theoretically, the total

charge (Qe� 201 pC) generated at the short-circuit system

during the mechanical deformation of BPNG can be

described as

Qe ¼ AsrYd3j; (4)

where As is the surface area of the piezoelectric material, ris the strain, Y is the Young’s modulus, and d3j is the piezo-

electric charge constant (5.5 pC/N) induced polarization in

direction 3 (Z-axis) of a three dimensional coordinate sys-

tem; the subscript ‘j’ denotes direction 1 (X-axis) or 3

(Z-axis) of the induced strain.33 It should be noted that the

d33 value of collagen arises because it displays a piezoelec-

tric response mainly executed in the axial direction, rather

than radial. To validate this output voltage and to demon-

strate the excellent integratability performance, linear super-

position tests were performed. Thus, at first, two BPNGs

were integrated serially and placed as layer stacking (inset of

Figure 3(b)) to be impacted simultaneously by hand slap-

ping. In this case, the output voltage is simply added up to

give Voc� 8 V. A largely enhanced Voc� 11 V by integrat-

ing three BPNGs and Voc� 14 V by integrating four BPNGs

in serial configuration are observed (Figure 3(b)). The slight

loss of output could be attributed to the leakage of electric

charge through the connection of the circuit. To understand

the observed piezoelectric response in terms of ultrasensitiv-

ity and output voltages, in this approach, the interaction

behaviour between the applied external stress and BPNG is

qualitatively predicted by finite element method (FEM) sim-

ulation conducted by the COMSOL multiphysics software.

To perform the FEM simulation model, a geometrical con-

figuration was considered where the fixed constraint is the

lower electrode and the bottom of the BPNG was electrically

grounded (supplementary material, Figure S9a). To simplify

the simulation, an external boundary load (ra� 0.17 MPa)

was applied to the upper electrode, and other boundaries of

the BPNG were considered as symmetric. The detailed simu-

lation process is described in supplementary material, Figure

S9, Table S3, and Associate discussion S4. It not only shows

the close proximity of simulated piezopotential distribution

(supplementary material, Figure S9d) with our experimental

observation but also reveals the resulting deformation (i.e.,

displacement) distribution of BPNG at the ra� 0.17 MPa

(Figure 3(c)). Interestingly, the maximum deformations

(�5.25 nm) occur at the upper edge portions of the BPNG

during application of ra to the upper surface. In FSC, though

the self-assembled peptide bonds are in a compact form, the

presence of air gap between the fibers makes the FSC porous

and soft.

This behaviour yielding considerably higher elongation

(i.e., displacement) in the upper edge portions than the mid-

dle portion of the FSC that leads to an increased piezoelec-

tric potential and its sensitivity. Effective electric power

output of the BPNG is obtained by measuring the output

FIG. 3. (a) Digital photograph of

BPNG driven by hand slapping. (b)

Generated rectified open circuit vol-

tages when the BPNGs (up to four) are

integrated in serial connection (shown

in inset). (c) Simulated total displace-

ment distribution of BPNG. (d) The

variation of output voltage and current

(inset shows corresponding equivalent

circuit diagram) as well as (e) effective

output power density as a function of

variable external resistances ranging

from 0.25–50 MX. The instant glow of

55 blue and 22 green LEDs are shown

in the inset. (f) The transient response

of an external capacitor connected to

BPNG via equivalent circuit diagram

(shown in the inset).

103701-4 S. K. Ghosh and D. Mandal Appl. Phys. Lett. 109, 103701 (2016)

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12:40:10

voltage as a function of the external load resistors (RL) rang-

ing from 0.25 MX to 50 MX (Figure 3(d)). Consequently,

output power density (P) is calculated as

P ¼ 1

Ae

:VL

2

RL

; (5)

where Ae is the effective contact area, and VL is the voltage

drop across load resistance RL. The output current (IL) is

found to be reducing across the incremental RL, depicted in

Figure 3(d), which is evaluated from

IL ¼ffiffiffiffiffiffiffiffiPAe

RL

r: (6)

The variation of P with RL is shown in Figure 3(e), where as

high as 1.14 lW/cm2 is obtained at the RL of 5 MX. At this

condition, a superior instantaneous piezoelectric energy con-

version efficiency (gpiezo) of BPNG up to 46.7% is achieved

(supplementary material, Associate discussion S5). In accor-

dance with such high P and gpiezo, layer by layer serially inte-

grated four BPNGs are enabled to instantly turn on more than

50 blue light emitting diodes (LEDs) displaying the letters

“ONPDL” and 22 green LEDs showing the letters “JU” (inset

of Figure 3(e)) by repeating gentle hand slapping impact,

where external storage devices, such as capacitors or batteries,

are not required. Moreover, BPNG is also able to charge up

an external capacitor (Ce� 1 lF) up to the charging voltage

(Vc) 1 V only in 30 s (Figure 3(f)) where Ce was connected

via parallel connection through a full-wave bridge rectified

circuit (inset of Figure 3(f)). Overall, a potential applicability

of BPNG as an energy harvesting power source can be con-

cluded to be interesting as across variable resistors, VL is

found to be sensitive to the large range of resistance. The

result fits well with linear circuit theory (supplementary mate-

rial, Figure S11 and Associate discussion S6) and gives rise to

3.5 MX internal resistance of BPNG. The equivalent circuit

model, shown in the inset of Figure 3(f), indicates that BPNG

can also be considered as a charge (q) source in parallel with

an internal capacitor (Ci).33 Considering the RC circuit model,

the evaluated internal capacitance of the BPNG is 3.43 lF

(supplementary material, Associate discussion S7). Relatively

higher internal capacitance with relatively smaller resistance

and also smaller optimum resistance (RL � 5MX) of the

BPNG is another advantage in the impedance match for

improving the piezoelectric response, leading to numerous

potential applications ranging from healthcare monitoring to

robotics.

In summary, the origin of intrinsic piezoelectricity from

FSC and underlying physics is spotlighted, besides this the

possibility of mechanical energy harvester fabrication, such as

BPNG, has also been proposed. It enables to capture several

forms of abundant ambient vibration motions available around

us. Owing to the distinctive features of high sensitivity, good

stability, and efficient piezoelectric power-generating perfor-

mance, BPNG may open an era in the field of self-powered

implantable medical device, surgery, e-healthcare monitoring,

and in vitro and in vivo diagnostics apart from its broad range

applications in personal portable electronic devices.

See supplementary material for further experiment and

simulation details.

This work was financially supported by a grant from the

Science and Engineering Research Board (SERB/1759/2014-

15), Government of India. The authors are also grateful to

DST, Government of India, for awarding INSPIRE fellowship

(IF130865) to Mr. Sujoy Kumar Ghosh. They also thank Dr.

D. K. Shukla and Dr. D. M. Phase, particularly for providing

the NEXAFS facility (BL-01 beamline, INDUS-2), and those

who helped in several aspects to carry out this work.

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