A new biosensor reliably detects pancreatic cancer
October 31, 2018
By Elton Alisson | Agência FAPESP – Pancreatic cancer, which is very rare in Brazil, is highly lethal because diagnosis is difficult and the symptoms tend to appear when the disease is advanced and resistant to treatment.
Efforts to achieve early diagnosis include routine screening based on blood or urine tests. These tests could increase survival rates for patients who are predisposed to pancreatic cancer or already have the disease but are asymptomatic. However, the available tests are expensive and inaccurate.
This situation could change, thanks to a biosensor created by researchers at the University of São Paulo’s São Carlos Physics Institute (IFSC-USP) in Brazil, with the participation of colleagues at the National Nanotechnology Laboratory (LNNano), the National Energy and Materials Research Center (CNPEM) and the Barretos Cancer Hospital, as well as Portuguese researchers affiliated with the University of Minho.
The scientists built a potentially low-cost immunosensor capable of detecting the main pancreatic cancer biomarker with high sensitivity and selectivity.
“We succeeded in producing an inexpensive biosensor that detects the antigen CA19-9, the usual pancreatic cancer biomarker, in actual blood samples and tumor cells at clinically relevant levels,” said Osvaldo Novais de Oliveira Junior, a professor at IFSC-USP and one of the creators of the device, in an interview given to Agência FAPESP.
The device consists of two superimposed nanometric films, one made of 11-mercaptoundecanoic acid (11-MUA) and the other comprising an active layer of anti-CA19-9 antibodies. A nanometer is a billionth of a meter.
CA19-9 is a glycoprotein synthesized by pancreatic cancer cells as well as normal cells of the pancreas and bile ducts. This protein is used as a biomarker of pancreatic cancer because it is typically found at high levels in people with the disease.
CA19-9 is usually detected with a blood test called an ELISA (enzyme linked immunosorbent assay) based on specific interactions between an antigen and the corresponding antibody. However, the high cost and limited sensitivity of this method prevent its use in the detection of early-stage pancreatic cancer.
“The antigen CA19-9 isn’t entirely specific for detection of pancreatic cancer. Production of the antigen may also be altered in patients with pancreatitis [inflammation of the pancreas],” Oliveira Junior explained.
The active layer of antibodies capable of recognizing CA19-9 in the immunosensor is deposited on top of the 11-MUA layer. The two nanometric films rest on interdigitated gold electrodes (electrical conductors) printed on a glass microscope slide.
When a blood or tumor cell sample from a patient is placed on the biosensor, the active antibody layer interacts with the CA19-9 layer to generate an electrical signal. The intensity of this signal indicates whether the level of CA19-9 in the sample is abnormally high.
“We produced the immunosensor with the simplest possible anti-CA19-9 antibody immobilization architecture. In order to obtain high sensitivity to the antigen, previous immunosensors had more complicated architecture, used more materials and involved more construction stages,” Oliveira Junior said.
Despite the simplicity of the device, its ability to detect CA19-9 was found to be competitive with similar but more sophisticated sensors, including others developed previously by the same group of researchers.
The new immunosensor could identify the antigen in commercial samples with a detection limit of 0.68 units per milliliter, as well as distinguish between blood samples from patients treated at the Barretos Cancer Hospital with different concentrations of CA19-9.
In experiments to evaluate the immunosensor’s selectivity for the antigen, it could also distinguish CA19-9 from possible contaminants.
“The results confirmed the immunosensor’s high selectivity and robustness, which reduce the risk of false positives, and proved that the device is highly sensitive only when there is interaction between the antibody and antigen,” Oliveira Junior said.
Barriers to use
In the researchers’ assessment, the results of their experiments with the immunosensor confirmed that the technology is sufficiently mature for use in clinical practice. However, important challenges must still be surmounted before this type of device can be widely used.
The first is the engineering challenge of mass production of sensing stripes with reliably similar responses. The second challenge relates to the analysis of the data generated by the tests to establish detection standards.
According to Oliveira Junior, this analysis can be performed by means of computational techniques that produce graphical views of the data and via attribute selection so that part of a signal generated by a test can be chosen as a basis for pattern distinction. “This part of the development will require integrated research by computer scientists and analytical chemists,” he said.
The article “A simple architecture with self-assembled monolayers to build immunosensors for detecting the pancreatic cancer biomarker CA19-9” (doi: 10.1039/c8an00430g) by Andrey Coatrini Soares, Juliana Coatrini Soares, Flavio Makoto Shimizu, Valquiria da Cruz Rodrigues, Iram Taj Awan, Matias Eliseo Melendez, Maria Helena Oliveira Piazzetta, Angelo Luiz Gobbi, Rui Manuel Reis, José Humberto T. G. Fregnani, André Lopes Carvalho and Osvaldo N. Oliveira Junior can be read by subscribers to the journal Analyst at: pubs.rsc.org/en/content/articlelanding/2018/an/c8an00430g#!divAbstract.