1. Introduction
A huge number of indispensable functions in human body are realized with
the support of proteins, for which amino acids form the rudimentary
building block. The distribution of amino acids in protein also
regulates the grade and freshness of numerous foods. A notable operation
that results in the emission of malicious aura in the outer atmosphere
is anaerobic digestion, which is achieved by microbes on amino acids.
Many compounds are produced as a result of amino acid catabolism
[1], out of which we have concentrated on the two products –
Volatile Fatty Acid (VFA) and amines. The deduction behind the catabolic
reduction of amino acid to VFA and amines are accounted to be
deamination and decarboxylation, respectively. Rappert and Muller
[2] reported in their review article, which galvanized us to explore
these three products – amino acid, VFA and amines. To be precise, the
chief molecules chosen for the current work are asparagine (amino acid),
lactate (VFA) and putrescine (amine). Asparagine is a non-essential
amino acid, which is demanded by humans for the growth of brain. Some of
the animal sources of asparagine are beef, eggs, poultry, diary, fish,
whey and so on. Moreover, this amino acid is found to exist in potatoes,
soybean, asparagus, corn, rye, maize, etc., [3, 4]. In concordance
with the expected structure of amino acid, asparagine is reported to
have an alpha-carboxylic acid group, alpha-amino group and a unique
carboxamide sidechain (CONH2). The molecular formula of
asparagine, comprising the above-said groups is
C4H8N2O3and the vapor pressure is computed to be 4.8 x 10-8 mm
Hg at 25 oC. Owing to the supreme nitrogen to carbon
ratio, asparagine is accounted to be a productive choice for nitrogen
transport and storage mechanism [5]. The possible sensing strategies
previously employed for detecting asparagine amino acid are High
Performance Liquid Chromatography (HPLC) [6] and MALDI/TOF-mass
spectrometry (MS) [7]. The anaerobic deamination of the amino acid
(present in vegetables and animals) lead to an intermediate product,
VFAs which in general is wielded in a variety of industries
manufacturing plastics, paints, fuels, textiles, pharmaceuticals and so
on [8]. The VFA – lactate
(C3H6O3) is regarded to
be a bio-indicator owing to the physiological roles played by it in
human body. The presence of lactate in blood, sweat, plasma and urine is
utilized to witness the changes in the health of human body viz., sepsis
[9], muscle fatigue, wound repair [10], acidosis, decubitus
ulcers [11], etc. Besides, 0.5 to 2.0 mM is recorded to be the
regular concentration range of lactate in the blood of human beings
[12]. Moreover, higher the concentration of lactate in human body,
higher is the risk associated with the human beings [13]. The
formerly reported detection methods of lactate are HPLC,
electrochemical-based, potentiometer-based and electro-chemiluminescent
detection [14]. Microbial decarboxylation of amino acids leads to
the release of a polyamine known as putrescine [15], which is noted
to be a food quality indicator owing to the harmful impacts induced by
it on the health of human beings upon the amplification of its level
[16]. The polyamine with the molecular formula
C4H12N2 possesses
hydrophobic methylene group and cationic demeanor. It is observed to be
useful for the growth and proliferation of cells, bacteria and
eukaryotes. In addition, certain physiological functions like
collaboration of ribosomal subunits, alteration in the chromatin state,
sustentation of tRNA structure, etc, are fulfilled using putrescine. To
detect putrescine, several well-known techniques like HPLC, ion-exchange
chromatography, capillary zone electrophoresis, colorimetric-based and
capillary GC are used [17, 18]. The mode of sensing handled by us is
of chemi-resistive type, which wields two-dimensional nanomaterials
(2DNMs) as a fundamental component. The logic behind the preference of
2DNMs for the detection of amino acid, VFA and polyamine is that 2DNMs
enjoys the advantage of extravagant surface area, which aids in intense
physisorption of the bio-molecules. In addition, many marvellous
attributes like malleability, optical transparency and pint-size of
2DNMs make them desirable. Moreover, the literary evidences recommend
the exploitation of 2DNMs to identify the availability of bio-molecules
– amino acid, VFA and polyamine. Some of the attestations include DNA
nucleotide adsorption on graphene nanoribbons [19]; tyrosine and
phenylalanine adsorption on graphene, graphene oxide and boron nitride
[20]; histidine, aspartic acid, arginine, glycine, lysine, alanine,
proline, glutamic acid, phenylalanine, tyrosine on graphene [21];
glycine, phenylalanine, histidine and glutamic acid on
graphdiyne/graphene [22]; tryptophan, histidine, phenylalanine,
tyrosine on graphene and single walled carbon nanotubes [23]. These
documentations actuated us to find out a capable 2DNM to sense the
presence of the amino acid – asparagine, VFA – lactate and polyamine
– putrescine. One of the attractive 2DNM, which is known for its
level-constrained band gap is phosphorene, a single layer of group-VA
phosphorus (P) atoms. The tri-coordination of P atom together with itssp3 type hybridization makes this 2DNM –
phosphorene to have various kinds of conformations. Initially, α
(black), β (blue), γ and δ-type of phosphorene were reported, followed
by a variety of allotropes namely ζ, ε, λ (green), η, violet phosphorene
and Kagome-form. Experimental realization of β-phosphorene and violet
phosphorene by molecular beam epitaxy [24] and exfoliation [25]
correspondingly encouraged the scientific community to persist many
researches on this 2DNM [26-30]. Among the wide range of available
allotropes, we have selected Kagome-form of Phosphorene (Kagome-P) as a
fundamental component due to the spectacular characteristics exhibited
by the material. The vigor demeanor of the 2DNM (Kagome-P) is observed
owing to the geometry of the material, which follows both the α-P and
β-P conformations. By perceiving the novel Kagome-P from side sight, α-P
conformation is reckoned which is attributed to the interaction of a
single P atom with two P atoms of the same level and one P atom of the
second level. Also, every P atom in β-P conformation is being superseded
by a triangle of P atoms. Experimental realization of Kagome-P can be
carried out through polymerization mechanism [31] and compressive
in-plane strain-based derivation mechanism (from β-P) [32].
Moreover, appealing attributes of Kagome-P like desirable absorption
coefficient (105 cm-1), wide-ranging
band gap and strain-based band gap transition prepare the 2DNM to be
operated in many optoelectronic devices. We studied the sensing
properties of phosphorene nanotubes and nanosheets to vapors
[33-37]. The ability of the 2DNM to take various forms like
nanosheet, nanotube, nanoribbon, etc, without losing its stable 2D
nature [38] along with the above-stated fascinating points impelled
us to investigate the interaction of the bio-molecules – amino acid
(asparagine), VFA (lactate) and polyamine (putrescine) on the
Kagome-form of phosphorene nanotube (Kagome-PNT).