Citation: Sompark, C.; Chawjiraphan,
W.; Sukmak, M.; Cha’on, U.;
Anutrakulchai, S.; Pongprayoon, P.;
Putnin, T.; Pimalai, D.; Pinrod, V.;
Japrung, D. Effects of Boric Acid and
Storage Temperature on the Analysis
of Microalbumin Using
Aptasensor-Based Fluorescent
Detection. Biosensors 2022, 12, 915.
https://doi.org/10.3390/bios12110915
Received: 15 September 2022
Accepted: 18 October 2022
Published: 24 October 2022
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Article
Effects of Boric Acid and Storage Temperature on the
Analysis of Microalbumin Using Aptasensor-Based
Fluorescent Detection
Chalermwoot Sompark
1,2
, Wireeya Chawjiraphan
1
, Manatsaphon Sukmak
3,4
, Ubon Cha’on
3,4
,
Sirirat Anutrakulchai
4,5
, Prapasiri Pongprayoon
6,7
, Thitirat Putnin
1
, Dechnarong Pimalai
1
, Visarute Pinrod
1
and Deanpen Japrung
1,
*
1
National Nanotechnology Center (NANOTEC), National Science and Technology Development
Agency (NSTDA), Thailand Science Park, Pathumthani 12120, Thailand
2
Postharvest and Processing Research and Development Division, Department of Agriculture,
Bangkok 10900, Thailand
3
Department of Biochemistry, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand
4
Chronic Kidney Disease Prevention in the Northeast of Thailand (CKDNET), Khon Kaen University,
Khon Kaen 40002, Thailand
5
Department of Internal Medicine, Faculty of Medicine, Khon Kaen University, Khon Kaen 40002, Thailand
6
Faculty of Science, Department of Chemistry, Kasetsart University, Chatuchak, Bangkok 10900, Thailand
7
Center for Advance Studies in Nanotechnology for Chemical, Food and Agricultural Industries, KU Institute
for Advance Studies, Kasetsart University, Bangkok 10900, Thailand
* Correspondence: deanpen@nanotec.or.th; Tel.: +66-117-6665
Abstract:
The instability of human serum albumin (HSA) in urine samples makes fresh urine a
requirement for microalbumin analyses using immunoturbidimetry. Here, we determined the ability
of an aptasensor-based fluorescent platform to detect microalbumin in old, boric acid-preserved
urine samples. Our results show that the cleavage site of protease enzymes on urine albumin protein
differed from the binding position of the aptamer on HSA protein, suggesting the aptasensor may be
effective for albumin detection in non-fresh urine. Furthermore, the addition of boric acid in urine
samples over a short term (at ambient temperature (T
a
) and 4
◦
C), long term (
−
20 and
−
80
◦
C), and
following freeze–thawing (1–3 cycles) did not significantly affect albumin stability, as analyzed using
the aptasensor. Therefore, boric acid stabilized has in urine stored over a short- and long-term. Thus,
the aptasensor developed by us is applicable for HSA detection in boric acid-preserved urine that has
been stored for 7-d at T
a
and 4
◦
C, and in the long-term at −80
◦
C.
Keywords:
boric acid; storage temperature; microalbumin; graphene oxide-based fluorescent detection
1. Introduction
Albumin is usually found in blood plasma and helps maintain the osmotic pressure
between blood vessels and tissue [
1
]. It can also act as a carrier of materials necessary for
controlling blood clotting [
2
]. Albuminuria is a pathological condition in which there is an
abnormally high concentration of albumin in urine [
3
,
4
], which is a sign of liver cirrhosis
in patients with chronic hepatitis and chronic kidney disease (CKD) [
5
,
6
]. The albumin
concentration in the urine of healthy adults is <30
µ
g/mL, whereas in microalbuminuria, it
ranges from 30 to 300
µ
g/mL. Albumin concentration is therefore one of the biomarkers
for abnormal kidney function [7,8].
The standard tests for urine albumin detection in hospitals are immunological-based as-
says, such as immunonephelometry, radioimmunoassay, and immunoturbimetry assays [
9
].
These assays require anti-human albumin antibody to form an albumin–antibody binding
complex, creating a turbidity signal; this signal is used to determine the concentration of
urine albumin. Although immunological-based assays are highly sensitive, they require
Biosensors 2022, 12, 915. https://doi.org/10.3390/bios12110915 https://www.mdpi.com/journal/biosensors
